BISON DEPARTMENT OF THE ARMY PAMPHLET NO. 1-54 1Ls 0101 .-n •-st q'g- WORK SCHEDULING TECHNIQUES HEADQUARTERS, DEPARTMENT OF THE ARMY MARCH 1968 Pam 1-54 FOREWORD The acquisition of Army materiel is a complex process involving numerous technologies, agencies, firms and personnel. Increased emphasis on life cycle management and systems effectiveness have necessitated even closer coordination of these diverse factors by Army managers. The demand for more efficient scheduling techniques to insure timely acquisition is a never ending requirement within today's advancing technology. Recent defense requirements have stimulated the gener3Jtion of numerous scheduling systems, each offering promise for improving project management. This pamphlet discusses the environment confronting the Army acquisition manager, including the life cyCle concept, life cycle milestones and the current management organiz3Jtion structures used. Each of the major scheduling techniques currently available are then surveyed and evaluated as to their effectiveness within the various phases of the life cycle. The pamphlet should be of interest to those involved in scheduling, ranging from first-line supervision through syStem project offices and headquarters groups. Itshould also be useful in schools or training organizations that instruct personnel in the use of scheduling techniques. Hopefully, it will stimulate effoxts to advance the state of the ·art in scheduling techniques, either by incremental improvements on existing techniques, or through development of substantially new systems. Suggestions for improving this pamphlet should be forwarded through channels to the Comptroller of the Army, Department of the Army, Washington, D.C. 20310. Pam 1-54 PAMPHLET) HEADQUARTERS DEPARTMENT OF THE ARMY No. 1-54 WASHINGTON, D.C., 13 March 1968 WORK SCHEDULING TECHNIQUES CHAPTER 1. INTRODUCTION Paragraph Page Purpose________________________________________________ 1-1 1-1 Scope__________________________________________________ 1-2 1-1 Materiel Acquisition Environment________________________ 1-3 1-2 Scheduling Process______________________________________ 1-4 1-11 Criteria for Comparison of Alternative Scheduling Techniques_ 1-5 1-12 Missile System Development Example_____________________ 1-6 1-13 2. BASIC SCHEDULING CHARTS Process Charts__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2-1 2-1 Leadtime Charts________________________________________ 2-2 2-1 Gantt Charts___________________________________________ 2-3 2-2 Milestone Charts___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2-4 2-7 Man-hour Load Charts__________________________________ 2-5 2-8 3. LINE OF BALANCE (LOB) TECHNIQUE Objective______________________________________________ 3-1 3-1 Program_______________________________________________ 3-2 3-1 Progress_______________________________________________ 3-3 3-1 Line of Balance_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3-4 3--3 4. NETWORK TECHNIQUES Work Breakdown Structure _____________________________ _ 4-1 4-1 Network ______________________________________________ _ 4-2 4-3 Time Estimates________________________________________ _ 4-3 4-6 Critical Path__________________________________________ . 4-4 4-6 Scheduling and Manpower Loading _______________________ _ 4-5 4-8 "Crashing" the Network ________________________________ _ 4-6 4-10 Network Families ______________________________________ _ 4-7 4-11 Evaluation of Networking _______________________________ _ 4-8 4-13 5. OTHER SCHEDULING CONSIDERATION Manpower Capacities vs. Manpower Requirements _________ _ 5-1 5-1 Multiproject Scheduling _________________________________ _ 5-2 5-2 Application of Multiple Scheduling Techniques _____________ _ 5-3 5-2 Learning Curves ________________________________________ . 5-4 5-3 6. SCHEDULING MANAGEMENT DATA FOR DECISION MAKING Decision Milestones_ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6-1 6-1 Special Studies__________________________________________ 6-2 6-1 Planning Data Requirements_____________________________ 6-3 6-5 APPENDIX ________________ c_________________________________________ A-1 Pam 1-54 CHAPTER 1 INTRODUCTION 1-1. Purpose a. This pamphlet is designed to illustrate • How and where work scheduling techniques can. be used in the Army materiel acquisition process. • How these techniques can a8Sist in the management process. b. This pamphlet is also designed to develop a more comprehensive understanding of these techniques by those persons • Who are in a position to use or direct the use of these basic management aids. • Who should be obtaining the benefits thlli't application of these work scheduling techniques oan provide. h-2. Scope a. This pamphlet is intended primarily for middle and lower level management personnel who are responsible for projects associated with the acquisition of Army materiel. Personnel so involved may be associated with • Headquarters, Class I or Class II installations. • Government or contractor plants. • Functional, project, or commodity managers. • Small projects or portions of larger projects. b. Subjoot matter selected for inclusion in this pamphlet is based on the following considerations. (1) Scheduling techniqueB. • Selection Coverage limited to the basic and proven techniques. Numerous adapt!l!tions or modifications of the basic techniques have not been include«l since there is no diffenmce in essential characteristics. • Coverage Limi'ted to simple descriptive material, including an example for each technique. Identification of principle technique characteristics and considerations for applicllition. Recognition that scheduling and its associated techniques represent but one of the fundtions involved in planning and controlling the expenditure of resources. • Application For planning and controlling the use of men, materiel, and equipment. For planning and controlling generation of management data for decisionmaking. • References Primary sources for additional detailed information are identified. Pam 1-54 (2) Acqwisiflion environment. • Coverage Simple descriptive material to establish the identity af scheduling techniques with real world problems. • Army Doctrine Restatement of Army doctrine, policy, and procedures is not a primary purpose of pamphlet. Necessary to establish how scheduling techniques can assist in implementing Army doctrine, policy, and procedures. • References Identification of basic Army regulations and pamphlets that cover doctrine, policy, and procedures. · 1-3. The Materiel Acquisition Environment The Army materiel acquisition environment is a dynamic, challenging process. Effective economical materiel acquisition demands continually modernized management. Managers must be alert to this environment and must keep abreast of the available tools and techniques that can· assist them in their materiel acquisition responsibilities. The use of effective work scheduling techniques is one means by which managers may meet and discharge their responsibilities with optimum reward. However, prior to any discussion of the basic· work scheduling techniques, it is necessary to briefly discuss the materiel acquisition environment. within which Army managers are placed. This environment consists of the following: · • The basic management process. • The life cycle concept. • The life cycle milestone concept. • The management organization structure. a. The Basic Management Process. The scheduling and control techniques discussed in this pamphlet are tools to be used by managers in given phases of the basic management process. To provide a proper framework for later discussion of these tools or techniques, a sound concept of the management process . will be presented in this section. This management process occurs in any organization at all levels of management and throughout the materiel acquisition environment. The fUilOtion of management entails continuous direction of others by determining and communicating the prime and supporting objectives of an organization. This function includes development of an integrated time-phased plan of action, which specifies needed resources and attempts to balance the demands for the resources over time. The basic steps of this process are shown in figure 1-1, and discussed below. Establish Objectives Determination and definition of objectives is the initial and most important step in the management process, la.rgely because the objectives of an organization are its sole reasons for existence. All organized activity must have as its motivating and guiding force the attainment of some predetermined objootive or objectives. The current purpose or purposes of the organization must be the yardstick against which all requirements and accomplishments are measured and evaluated. The progressive passing down of specific coordinated objectives Pam 1-54 MANAGE1v1ENT PROCESS Figure 1-1. from higher to lower levels of management sets targets and authorizes detailed planning effort on the part of receiving organizations. Develop Plans Given the determination or assignment of an objective, the next step is development of a plan. The planning function sets forth the nature, sequence, and interrelationships of the secondary objectives that support the prime objective. Planning at each level specifip_s the kind, qualit.y, and quantity of work units in support of objectives. This plan must be consistent with available resources and time. Ifthe planning is not accomplished, there can be no assurance of coordinated balanced use of resources. The overall plan establishes rthe feasibility of meeting the directed due date for the prime objective. Though this plan considers resources required over time, it does not consider the competition for these resources. Determ,ine Sched~tles Scheduling is the bridge between planning and implementation. It is the translation of the plan, with its elapsed time estimates, into calendar time. The scheduling function considers the competition for available resources both within and between programs. Ifthe earliest attainable schedule completion date of the current plan is later than the desired date, the manager will usually refer the proposed schedule to the planners for readjustment. If the planners cannot achieve this, they must obtain a new completion date from the next higher level of management. The goal of the scheduling function is to produce a calendar time-phased plan consistent with desired completion dates for the assigned objectives. This schedule is the vehicle for authorizing effort and resources to be expended. It serves as a basis for the continuous evalu'ation of progress. Evaluate Progress Once the scheduled plan has been activated, a formal procedure for the regular reporting of progress against scheduled plan is necessary. There must be a process for identifying potentially significant problem areas early enough so that there is still time for management to seek solutions to that problem. The management process emphasizes, therefore: • Regular, continuous evaluation of actual performance against current scheduled plans. Pam 1-54 • Detection and isolation of significant deviations from the scheduled plan as a forecast of time and cost overrun. The principle of "significant reporting" effects a great reduction in the volume of statistical reports. By considering only the significant deviations from the scheduled plan, the manager need only analyze the problem in terms of: • What remedial action is being taken and by whom~ • What results may be expected and when? Management Decisions and Action.~ The magnitude and relationships of all desired chang~ must first be examined in the light of their effects on the scheduled plan. Changes may result from alteration in prime objectives or isolation of the problems at any level of effort. Where the changes originate is not so important as an orderly and authoritative method of approval and implementation. Deviations from the scheduled plan may require only a change in schedule. Deviation could, however, require a change in plans, or even a change in objectives. Adequate communications are required to insure that changes are received and understood across all levels. A clear distinction must be made as to new action that is within the authority of the operating organization and action that calls for lateral or higher authority. The first can be handled by direction; the second calls for a careful presentation of the :facts and a request for the action desired. Recycle The incorporation of change is achieved by a recycling of the management process to provide a revised scheduled plan. Dynamic recycling is the method of achieving and maintaining objective-oriented management control The formal progress, review and evaluation meetings held by management with supporting managers provide an opportunity to accomplish the mechanics of the recycling process. Summary The management process is constantly in motion at all levels of management. Although the problems change in character and the management systems or techniques vary, the basic process remains unchanged. In addition, the management process occurs within each major phase and throughout the life cycle of Army materiel. A brief discussion·of the life cycle concept will relate how the management process occurs within the cycle. b. The Life Cycle Concept. The typical materiel life cycle extends about 30 years from the time research is conducted. The life cycle includes adopting products of research for use in an item (such as weapon or equipment systems); developing, producing, and fielding the item or system; and then finally disposing of it as obsolete. This is not to say that the same system or weapon is in operation :for 30 years before a new one is developed. In :fact, a new item is usually developed and produced 111bout every 9 years. There are six ph~ses in the materiel life cycle used by Army (fig. 1-2). They are: the concept formulation phase, the contract definition phase, the development phase, the production phase, the operational phase, and the disposal phase. Pam 1-54 LIFE CYCLE SPECTRUM X--POINT IN TIME II~' I<'·'1::5 JW#;.:w/21'"" 0 ~""' TRANSPORTATION D INSPECTIDN SYIIBOLS (ASIOE) D DELAY v STORABE D CDIIBINATIDN Figure 2-1. ]east 21 weeks prior to project finish-because the tasks between control points 4 and 15 are expected to take 21 weeks. Because great ·care is needed to assure that tasks tie together at the proper time, leadtime charts are more difficult to construct than process chRrts. 2-3. Gantt Charts The Gantt chart is the cornerstone of the Gantt technique, the first formal scheduling system to be used by managemenf.l The Gantt chart. is basically a 1 Developed by Henry L. Gantt in the late 1880's, the technique was based on the scientific management approach of Frederick W. Taylor. Pam 1-54 LEAD TIME CHART flAil 'fiSIIIfl AllllffTIEl 11 S/q 1.2~--------------------, fAll/fAT£ IIPUII tm,tiT1/llf£fffD SIT£ tN{&I DIT IISTIIllflllIFtill#I £1111111£/T fAll/fAT£IIISSIL£TIAIS,ITAT/11 f£6/(l£/.1 Jllllf£fD SIT£ fJIII(JT£ /1/SSIL£ j 1I I 1) 1 1 1 1 1 I 1 1 1 1 1 1 1 ll 1 1 1 1 1 I I 1 lj I I I 1 1 1 1 I I I' I I I i1 I I I i 0 5 4'0 35 0 25 '0 15 10 Weeks Prior to Completion (LEAD TIME) Figure 2-2. bar chart or line chart with time graduations shown along the horizontal and people, organizations, machines or tasks shown along the vertical. The bars (or lines) show the time units of work that are scheduled for each person, organization, machine or task. The Gantt chart can be used to control the schedule as well as to portmy the initial schedule; progress on scheduled work is entered periodically; rmtsons for being ahead of or behind schedule may be shown, in coded form, on the chart; and from this the schedule may be updated. There a.re a number of variations of the Gantt technique, all of which use a form of the basic chart described aboYe. Two examples will be discussed in this pamphlet, one for nonrepetit.iYe production and the other for repetitive production. a. Application to Nonrepetitive Production. Figure 2-3 is a Gantt cha,rt showing scheduled activities for the hypothetical missile system development example. Note that each activity that is in a series cannot begin until the preceding activity is completed. Also, the chart shows the common practice of scheduling each activi'ty at its earliest possible start time. For example, consider activities 9-11 and 11-13: "Install missile at site" (11-13 obviously can't begin until "transport missile to site" ( 9-11) has been completed). There is nothing that says missile installation must begin right after transportation, but it is common practice not to delay it. Activity 1-2, "train operating personnel" is the only exception to the pvactice of starting an activity as early as possible. It is shown starting 5 weeks after the stMt of the project so that trained personnel will not be without work for long periods later in the project. The kind of Gantt chart in figure 2-3 is a very useful visual device for the manager. However, it does not show where the activities are to be performed: The manager needs to know this to pinpoint responsibility. Thus, it is common Pam 1-54 GANTT CHART NOII-REPETinVE PRODUCTION, AmVInES SCHEDUlE ACT. ACTIVITY IR. ! ,FAll/CAT£ IIISSII£1-5 TtAISPOITATIOI YEKICi'. PfliY£11/IISSil£TIAIS. 5-9 YEKICL£ TO IIISSIL£ FAll. IISTALLAT/011 1-4 &H£&1QUT £QUIP/£IT TEST IISTAllATIOI I 4-8 &KftlfiUTfiUIPim TIAIISPIIT IISTAll:~ 8-10 I tllf&IOUTliUIP.Tfl INSTALL &lll&IDIT 10-12 liU/PII£111 AT SIT£ FAll/CAT£ 1-3 UDUID EOUIPIIEIT TIAIISPDIT GIOUID 3-7 EOUIPII{IT T/J SITE flAil 1-2 OI'EIIATIIIG PEIIS/JIIfl TIAIISPOITDPEIIATIII 2-7 P£1SOIIIEL T/J SITE IISTAll 7-12 ti/JUID EOU/PII{IT &HlU/JilT IISTALLAT'I. 12-14 OFGIDUID £011/PIEIT FAlllUTE 1-6 /fiSSilE C/JIIIf&T OEFI&Ili&IES 6-9 II IISSIL£ TIAISP/JIT9-11 /fiSSilE TO SIT£ liSTAll 11-13 /fiSSilE AT SIT£ &H£&1 OUT /fiSSilE 13-14 IISTALLATIOI TIIAISFEIIESPOISIIIL· 14-15 ITT TO 1/SIIUDIIIAIO I I I WEEKS* 1.0 20 3p 4,0 ~0 I I 0 I 0 0 I 0 l 0 0 0 I I I 0 D I I [ *Time Scale May Be In Calendar Time Figure W. to further refine the Gantt chart to show where activities are performed. Figure 2-4 shows the same data and same schedule but rearranged to show what organization performs each activity. Activity numbers are shown for each bar on the chart, though at the projecit manager level this information may not be needed. The project manager is concerned with who has work to do and is it on schedule-never mind the details. The discussion in chapter 5 on manpower capacities versus manpower requirements explains how the quantity of work that an organization can handle is determined. Pam 1-54 GANTT CHART NON-REPETmVf PRODUmON, ORGANIZA nON SCHEDULE WEEKS GOV'T.OAOANIZATION OR ! CONTRACTOR 0 10 2p 30 40 5~ I I I IIJ/111& fttJfflllfiTJ 1-2 I I TIJISPfJITJT/61 ftQY'TJ 8-lo-0 []l-•7 JY-2-7' [!--?-" QP£1JTIIt P£1SfJII£l f&QY'T. ffi-3·14 13-14 I I COITIJ&TDI· 1-3 I &lOIII £1VIPI£1T &OITIJ&TOI·IISTJLLJTIII 1-4 1 4-8 I &11£&1111Elll'*fiT IE! ,,__5-9 &QITIA&TOI· 1/SS/i£ ' i TIAISPOITAT/01 Y£NI&i£ 1-5 &QITIA&TOI·IISS/i£ 1-6 6-9 1111-131 I i PIOJ£&T IAIA&£1 f&Qf'T.J 14-15-u ~ Figure 2-4. Figure 2-5 is the type of Gantt chart shown in figure 2-4 but with activity numbers left off to permit progress information to be entered without excess clutter. The chart shows progress on all work as of the lOth week (see arrow). Note that the contra-ctor for installation and checkout equipment has finished all of his work 6% weeks ahead of schedule-with the help of transportation. The contractor for the missile transportation vehicle is on schedule, and so is the training of operating personnel. The contractor for ground equipment is slightly behind, 'and the missile contra-ctor is quite a lot behind. A new progress report is prepared periodically-perhaps every week, may be less often. (The milestone technique, presented later, permits more economical progress reporting on a management-by-exception basis.) This pamphlet is not concerned with how the manager decides what to do about ahead-and behind-schedule work-only with providing the manager with the progress information he needs to make that decision. However, it should bP noted that managerial decisions often call for revising the schedule to more closely reflect what is actually happening. Because of pressure to meet the project completion date, schedule extensions that affect this date are made only as a last resort; i.e., if enough resources (manpower, money, etc.) cannot be added to put the project back on schedule. Noncritical a-ctivities, such as the ground equipment contractor's work, can be extended within limits without affecting the 50-week total project time. As mentioned earlier, the Gantt chart may also be constructed so that people or kinds of machines are listed in the left-hand column. A machine-oriented Gantt chart, for example, would be useful in scheduling a computer and auxiliary equipment in a data processing center. Being very expensive, the computer would probably be fully scheduled with work for 'three shifts first. Then 2-5 ' Pam 1-54 . GANTT CHART HOH-REPfTmVE PRODUCTION, PROGRESS REPORT GOY'T. ORGANIZATION OR CONTRACTOR TIAIIIIG ft/JY£11#£111 TIAISPQITATI/JI ft/Jr'TJ 0 0 0 •I I QPEIATIIt P£1S/JII£t I D t/JITIA&TOI· tiOII/1 £11/P#(IT &QITIAUOI·IISTAilATIQI AIO &K£&106! £QVIf#£1T &IJITIAfTIJI •#ISS/l£ TIAISPQITAT/11 Y£11/&l£ &/JITIA&TII· #ISS/l£ PIIJJflT #AIIAt£1 rt/Jr'T.J TIMF .NOW Figure 2-5. other machines-sorter, collator, printer, card punch, etc.-would be scheduled with any work needed to support the computer schedule. The reader has probably observed that the Gantt chart and leadtime chart are related. Both have a horizontal time seale and both sequence tasks in a similar manner. However, the differences should be noted. There are obvious minor differences in the way the time scale is numbered and in the task symbols used. A more significant difference is that the leadtime chart omits the left-hand column that classifies the tasks in some way. But'the main difference is that leadtime charts must show latest possible start times for tasks, whereas Gantt charts need not do this. Thus, in the Gantt chart, "fabricate missile transportation vehicle" is begun at the project start date though it could be delayed 26 weeks without affecting total project length. b. Application to Repetitive Prod1tction. The Gantt technique was originally developed to schedule and control repetitive production.1 Its application to nonrepetitive production was presented first since project management mainly involves single unit production. Occasionally, however, a project will involve a repetitive task. Since the missile system example hasn't any repetitive tasks, an example of repetitive packing of cartons will be used to demonstrate this Gantt application. The object will be to compare the actual rate that a packing section is packing cartons with a normal or standard rate. Assuming this comparison is made weekly, it is necessary, in order to arrive at the actual packing rate, to count the number of cartons packed for the week and divide it by the number of hours the packing section worked. For 1 Described in The Gantt Oha1·t, Wallace Clark, Sir Isaac Pittman & Sons, Ltd., London, third edition, 1952. Pam 1-54 example, if 800 carton were packed last week by five packers working a 40-hour week, the rate is 200 hours+800 cartons=0.25 hr per carton. Assume that the standard time for a man to pack a carton is 0.25 hr per carton.2 The packers have actually taken 0.05 hours too long per carton. Stated another way, they have packed only 800 per week instead of the standard of 1,000 per week (0.20 hr per carton X 200 hr per week). The manager would use this information to judge what the effects will be on other work and on final completion date(s). This would point out any need for corrective action; e.g., putting the packers on overtime. If packing is the only repetitive task in the project., it would probably not be worth while for the manager to display the information on a Gantt chart. Ifthere are several such tasks, however, the Gantt chart can save time in recording progress information and in analyzing it for possible corrective action. Figure 2-6 shows the data for the packing section plus two other hypothetical sections. The legend explains all of the progress information that is entered on the chart. In keeping with the management-by-exception principle, there are no symbols to explain ahead-of-schedule status-only the problems. Note that the bars and solid lines do not indicate the schedule. They indicate progress. The schedule is simply 200 cartons per day, day in and day out. Whereas the Gantt chart for nonrepetitive production is useful for visual display of related task schedules and progress, the chart :for repetitive production is useful only. :for progress purposes (fig. 2-4,2-5, and 2-6). Figure 2-6 may provide all the information the manager needs to control schedules. If the sections get seriously behind schedule, however, he may want more detailed information on what is happening within the sections. Figure 2-7 is a detailed breakdown of the summary data in figure 2-6. Itshows what manpower problems or machine problems' contribute to behind-schedule status. If the program manager is not interested in this, the section foreman certainly would be. The point of figure 2-7 is that Gantt charts for repetitive tasks can be constructed with different. degrees of detail for use by different levels of management. Table 2-1 summarizes the strengths and weaknesses of the Gantt tedhnique. 2-4. Milestone Charts In applying the Gantt technique to nonrepetitive production, the tasks or parts Of the program are sometimes described in gross terms. In figure 2-5, for example, activities 1-3, and 1-6 are large blocks of work. Regular reports of progress on the total activity can be subject to serious errors of estimation, and the practice of reporting regularly is not in accord with the management-byexception principle. It is more economical to report progress only when "milestones" are completed. A milestone may be completion of an entire short activity, like activity 7-12, "install ground equipment" (fig. 2-5). It may also be a part of a longer activity. "Fabricate missile," activity 1-6, for example, could be divided into two or more milestones. Figure 2-8 is an example of a milestone chart. It is like figure 2-4 except that in figure 2-8 the arrows showing when progress will be checked are at • The standard time may be someone's estimate as to how long it should take a typical worker to pack a carton; lt may be how long it has taken In the past to do similar work; or It may be an engineered time standard carefully developed through stopwatch time study or one of the other refined techniques. In any case, the standard time should Include an allowance for personal time, rest ~ime, and unavoidable delays. Pam 1-54 GANTT CHART REPETITIVE PRODUCTION SCKEDUL[O PRODUCTIOI liON. 8 IfED. g THUll$. CUTOI •Fe. SECTIOI 100 CARTOif$ 1'£11 DAY 100 PACIIIC SECTIOI CARTOif$ 1'~/tDAY STEICILIIC SECTIOI ~00 CAitTOif$ PER DAY J. -Amount of work actually done in a day. 2-IIIII Weekly total for section. 3-Reasons for falling behind: A~ Absent N • New Operator S • Slow Op6rator R • Repairs Needed T =Tool Trouble M • Material Delay Figure 2-6. s~lMW milestones. Progress is checked twice for activity 1-3, three times for activity 1-6 and only at scheduled completion for all the others. Thus, the total number of activity progress reports are 20 in figure 2-8; in figure 2-4 checking progress on each activity every week totals 120 activity reports. Each time progress is reported many people must take time to check out and estimate percent completions. Thus, the milestone technique of reduced progress reporting saves a great deal of time and money. Yet it reports progress when it is most needed-provided the milestones have been carefully selected. Table 2-1 applies to milestone charting as well as to Gantt charting. The additional advantage of milestone charting is the lower cost of progress reporting. 2-5. Man-hour Load Charts Man-hour load scheduling is a more flexible version of the Gantt application to nonrepetitive work. In manpower loading, task completion dates are specified but task start dates are not. Thus, those responsible may work on the task any time they wish, as long as it is completed at the end of the load period . . As an example of this idea, notice in figure 2-4 that activities 1-5 and 5-9 are scheduled to start at week 0 and finish at week 10-even though the missile Pam 1-54 GANTT CHART REPETITIVE PRODUCTION (Detail) AUGUST j SCHEDULED PRODUCTIOI liON. 1 TUES. 8 /flO. 9 THURS. 10 FRI. II~ &00 •T j • CARTDI lfC. CARTONS SECTIDI PEIID&Y 100/DAY IA&KII£ I I __. T IA&KIIf T 100/DAY J oiLN zoo ~A,5 ·~~ 5 -~ PACIIIC SECTIDI CARTONS ' PER DAY _. 5 5 5 5 5 ~ NAil 40/DAY ~ ~ 1111 40/DAY A IAI t 40/0AY IAI I 40/DAY ~. A N 1---N N ! IAI [ 40/DAY ~ ~ zoo - STEICILIIC CARTONS -= I SECTIOI PER DAY -_. ..... IAIS 110/DAY• llillllll[ IAN T •o/DAY. -M - iii * Man T also mov11s malerialand lhus Is TillE NOW. scht1dult1d for ft1wt1r carIons than man S. Figure2-'Y. transportation vehicle is not needed until week 35. The man-hour load technique could have been used instead. In this, the schedule would indicate the due date (week 35) and the number of weeks of work involved (10) but not the start date. The contractor could then do the work as it best fit in with his other soheduled work and capabilities. This places more responsibility for control onto the contractor and lessens the control powers of the project manager. Thet·e are two opposing points of view: The project manager would rather have the work start as early as possible (as soon as the contract is let) to assure that it will be done on time; but the contractor would rather have the flexibility to fit the work into the most economical time slot in his schedule. He would also rather control his own destiny than be tightly controlled by the project manager. From the Government's viewpoint, it is sometimes necessary to maintain tight scheduling and tight control in order to meet deadlines. This applies for complex and uncertain projects in which many blocks of work tie closely together. When task due dates nre less critica,l and task time estimates are more Pam 1-54 . Table 2-1. Gantt Technique-Strengths and Weaknesses Criteria 1. Accuracy_,_______ _ 2. Reliability_______ _ 3. Simplicity_______ _ 4. Universality of Project Coverage. 5. Decision Analysis__ 6. Forecasting______ _ 7. Updating_________ 8. Flexibility_______ _ 9. Cost____________ _ Strengths Good in repetitive work-time estimates likely to be good and production is easy to count. Simplicity of technique helps project manager to set up consistent progressing system. Easy to understand, to accept, and to implement. Effective at work center levels. Can cover well a given' phase of a life cycle. Shows clearly ability to meet schedules in repetitive work. Easy to update if program is static. Data gathering and display are relatively inexpensive. Weaknesses In nonrepetitive work accuracy of estimate of task completion percentage is subject to error. In repetitive work production count can be "doctored." Large nonrepetitive projects involve many different progress estimators, which tends to hurt consistency. Requires good time estimates or standards, which are not simple to develop. Not effective for large, complex projects. No capability to simulate alternatives. Does not readily show ability to meet schedule if many interrelated tasks are involved. Much chart reconstruction needed to show program changes. Frequent program changes cause costly redrafting of charts. · MILESTONE CHART NON-REPETmVE PRODUCTION, ORGANIZATION SCHEDULE WEEKS GOV'T. ORGANIZATION OR l CONTRACTOR ~ 10 ~0 30 4.0 50 I I I TIIA/1111 fi6Y£1111£1TJ 1-2 I J I TIIA/ISP#/ITAT/#1 fi#V'T.J [jP7~7 r:J.-Y-11 8-10-0 OP£/IAT/11 P£1SOII£i flfH'TJ 13-14 gj 12-14 I J .. .. COITIAlTOI 1-3 GI#QIO £1QIPII£1T I .., &OITIA&TQI-IISTAUATIIJI jg AIO &HE&IOQT EIQ/PI£11 1-4 1 4-8 .., &OITIA&TOI-11/SS!i£ 1-5 5-9 TIAISPIITAT/fJI Y£1/&i£ I .. .. &fJITIA&TDI-1/SSii£ 1-6 PlfJIE&TIAIAI£1 fiOf'T.J ., I 6-9 i111-1.1T • 14-15--q Figure 9!-8. Pam 1-54 certain, it is often better to schedule more flexibly using man-hour loading, thus releasing some of the control responsibility to operating elements. The charting of man-hour load schedules can be done in a number of ways, two of which will be presented. Figure 2-9 is like figure 2-4 except some of the activities have been man-hour loaded. For example, activity 1-3 is man-hour loaded. Itis shown as a shaded bar between weeks 10 and 29. This mea.ns that it should take 19 \Yeeks to do the work, and it must be finished by the 29th week. It need not begin at week 10 but may start anytime between weeks 0 and 10. Activity 3-7 following 1-3 is shown unshaded which means it will start precisely at week 29 and finish at week 30. Then the next activity, 7-12, is again man-hour loaded. It is shown between weeks 33 and 36, but it may start anytime between weeks 30 and 33. Progress reports for man-hour loaded activities would be in accord with where the bars are located on the chart. Thus, for activity 1-3 progress would not be checked until after the lOth week. If the activity actually began at week 0, the first progress report would occur at week 11-assuming weekly reporting-and would show ahead-of-schedule status. A more rigid variation of the man-hour loading is one that is sometimes called the load-by-schedule-period technique. It is quite commonly used by contractors or Government industrial installations in scheduling routed workwork done in support shops, like the wood shop, sheet metal shop, and welding shop. Figure 2-10 is a simplified chart showing three job orders scheduled into GANTT MANHOUR LOAD CHART. NON;RfPfTITIVf PRODUUION, ORGANIZATION SOIEDULE OOV 1T. ORGANIZATION OR CONTRACTOR 0 10 40 50 TIA/1111 ftlf£111£111 1-2 8-10--IJ:V' 0?-1 o-9-11 12-~ ""'"""""'n_.o ---------------( 13-14 &fJITIA&TfJI tlfJVIfJ £fJVII'I£1T &fJITIA&TII-IISTAUATifJI AU &11£llfJIIT £11/I'IFIT • &fJITIA&TII-1/SS/l£ TIAISI'IITAT/11 r£11/ll£ &#ITIA&TfJI-IISSil£ 1-6 f'I(JJ£&T /IAIAt£1 (/fJf7. I NOTE• Sht1ded bt1rs represent mDnhDur IDDdlng. NDn-Shtlded bt1T6 represtmf DTdinDTy fJDnff scheduling. Figure 2-9. Pam 1-54 two shops by this technique. In this example the schedule period length is 1 week. It could be 2 weeks, a month or any other convenient time frame. In the load-by-schedule period technique any operations shown within a schedule period must be done by the end of that period. They can start any time as long as that completion date is met. Thus, in figure 2-10 the sheet metal shop has 1 'veek to do the first operation of job orders 101 and 102; in that same week the welding shop has to do the first operation of job order 103. In the second week, the sheet metal shop does the second operation of job order 103, and the weldin_g shop does the second operation, of job orders 101 and 102. For job orders with many operations, the materiel is routed from shop to shop in this manner, each shop getting 1 week to accomplish its operation. Rush jobs, of course, v>ould not be scheduled this way. But the technique is useful for normal routed job-order production in that it allows shop foremen a great deal of flexibility in assigning work most economically. Unscheduled time remaining in a schedule period is available for last-minute rush jobs or for such things as internal shop maintenance. The strengths and weaknesses for the man-hour load techniques are the same as those shown in ta:ble 2-1 with a couple of exceptions: The man-hour load techniques provide greater flexibility bnt at a sacrifice in forecasting ability. GANTT----------- LOAD-BY-SCHEDULE-PERIOD CHART NON-REPETITIVE PRODUCTION, ORGAIIIZA TION SCHEDULE WEEKI WEEK2 SHEET METAL SHOP 101 1 102 103 I I WELDING SHOP 103 101 102 I T Figure 2-10. Pam 1-54 CHAPTER 3 LINE OF BALANCE (LOB) TECHNIQUE The line of balance (LOB) technique is useful in controlling complex repetitive production projects with a number of interrelated adt:ivities. It employs the.leadtime chart and the project delivery schedule in analyzing progress data for each control point. The line of balance shows what control points need attention now in order to maintain schedules in the future. Though there is also a versioi1 of LOB for nonrepetitive production, it is rarely used. The networking techniques have been found to be simpler and to provide more complete control of complex nonrepetitive production. The LOB technique will be explained below. The missile system example could not be used, since it is not an example of repetitive production. 3-1. Objective The first step is to draw the contract delivery schedule on what is called the objective chart. An example of an objective chart is shown in (a), figure 3-1. The chart shows cumulative units on the vertical and dates of delivery along the horizontal. The contract schedule 1 line shows the cumulative units to be delh·ered over time for the project. 3-2. Program The second step is to chart the program. The program, also called the production plan, is merely a leadtime chart, which was described in more detail in chapter 2. Only the most meaningful events should be selected as control points in making the leadtime chart. The leadtime chart for this example is shown in (b), figure 3-1. The 12 control points represent the key tasks in manufacturing one unit of a hypothetical product. The program tells us that initial purchasing (control point 1) must begin 24 working days prior to any scheduled delivery. Thus, purchasing must begin 24 working days prior to 1 January in order to meet the first scheduled delivery of five units by the end of December (see the objective chart). The leadtime for the other control points can be related to the delivery schedule in a similar manner. 3-3. Progress In controlling this program assume that the manager gets monthly status information for each control point. On the progress chart (c), figure 3-1, the bars show this status information as of the end of April. Thus, the bar for control point 12 shmYs that 14 units of the product have been assembled for deliYery. The bar for control point 9 shows that 40 of subassembly Bare ready for final assembly. The bar for control point 4 shows that in-house fabrication has begun on 60 of one of the required parts. The other control points can be 1 The term "contract schedule" should be Interpreted broadly to Include In-house production as well as contracted production. ., w SAMPLE LINE ol BALANCE CHART a ~ (a) OBJECTIVE ~ MONTH on: JAil &IIITIA&TS&lfPilt G 8 AtTIAl Ptll,tlf 0 5 I I If COWTRACT SCHEDULE~~ (CUIIULATIIIEJ v /· ./ ~ . ,.._ ~..:::.CTUAL OELIIII"RY FEB liAR I APR I IIAY JUN 15 20 30 &2 80 7 II I 14 ~ I Dote ofStudy--i-fMoy PURCHASE' PART 4 3 uNtrs -SO-l (c) PROGRESS -Jn,. --70-l------------------------~ -60 -50 40 -30--20-10 -o aaR FABRICATE PART INHOUSE 2 ,ASRICATE PART IN HOUSC 3 5 SUS-CONTRACT PART 'I iJ 22 II !P li II il 16 IS II ~ ~!l:t1.IS ~ ~ IS ~ ~ ;s: LINEOFB_ALANCEASOFIIIAY IS IS IS IS i!!< / §~S~S!s:;s:~ !Si, §~~~~~ ~ L 1~ ~~~I~ ~ §ISIS!s:;s:~§ ~ ~~~~~~~§~~!S;s< ~~~~~~~~~~~~ I 12 IJ' II I SI 6 I f II II I11111111111J IIIIlS 1111 If1111111111 (b) PROGRAM 7 8 SUB-ASSEMBLY "A'" SUB-ASSI'IIBLY '"B" 12 SHIP IJ i! II Ill I I f 6 S I j 2 I II WorkinQ days prior to shipment-22 work days per month Ji'igurc 3-.l. Pam 1-54 interpreted similarly. Progress on final deliveries has also been shown month by month onthe objective chart. 3-4. Line of Balance To analyze how present progress on each control point will affect :future schedules, the line o:f balance is constructed. The line o:f balance represents the number o:f units o:f the product that should have passed through each control point :for :future delivery schedules to be met. This line o:f balance is drawn on top o:f the bars on the progress chart in order to show status o:f control points. The difference between the line and the top o:f a bar :for a control point is the number o:f units behind or ahead o:f schedule. Thus, control point 12 is 16 units behind schedule, control point 9 is five units ahead o:f schedule, and control point 7 is 21 units behind schedule. Control point 12 is behind schedule as o:f now, 1 May, since there is no leadtime :for it. However, the main impact o:f control point 7 being behind schedule will be :felt 12 working days in the :future, which is the leadtime :for control point 7. That is, the insufficient number o:f subassembly "A's" started into production as o:f 1 May will adversely affect final deliveries 12 working days hence. All other control points are analyzed in the same 'vay. Delays at control point 7 may have been causing final delivery problems throughout the contract thus :far. However, the purpose o:f line o:f balance analysis is not to show what has caused present shipping slippage-that is water over the dam. Instead it is important to analyze the control points with a view to detecting potential troubles :for the :future. The line o:f balance is constructed in the :following manner : a. Select a control point, say 7. b. From the program ((b), fig. 3-1) determine the leadtime, the time :from the control point to shipment (i.e., 12 working days). c. Using this nUIIDber deterniine the date that the units now at the control point should be completed. (May 1 plus 12 working days is May 16.) d.· Find the point corresponding to this date (May 12) on the contract schedule line and determine how many scheduled completed units this represents (41). e. Draw a line on the progress chart ( (c), fig. 3-1) at that level (41 units) and over the control point (7). f. Repeat the above :for ea.ch control point and connect the horizontal lines over the control points. The resulting line is the line o:f balance. It indicates the quantities o:f units that should have passed through each control point on the date o:f the study (1 May) i:f the delivery schedule is to be met. With the LOB charts shown in figure 3-1 management can tell at a glance how actual progress compares with planned progress. Analysis o:f the charts can pinpoint problem areas. Updating the charts requires a good status reporting system, which can be mechanized i:f the project is large and· complex. A computer program has been developed by the Army Management Engineering Training Agency, Rock Island, Ill., that will provide printouts o:f all the information required on the LOB charts. Actually, since the program provides all the info:rnnation, the printouts could be used by themselves without the need for charts. Graphic display o:f the information is, however, usually desirable. Whereas the Gantt technique :focuses on efficient use o:f resources, the LOB technique is product oriented. Its key :feature is that bottlenecks in the production process are brought out. Management must then take proper action, gen 289-707 0 -68 -3 Pam 1-54 erally increasing-the resources at the bottlenecks. O>nsequently, Gantt and LOB are complementary techniques. Table 3-1 summarizes the strengths and weaknesses of the LOB technique. - Table 3-1. LOB Technique-Strengths and Weaknesses (In repetitive production) Criteria Strengths Weaknesses 1. Accuracy__________ Completion time estimates are good, since work is repetitive. 2. Reliability_________ Compares favorably with Gantt technique. 3. Simplicity_______________________________________ How the line of balance is con structed is not always understood. 4. Universality of Well suited only for production Project Cover-phase of life cycle. Does not age. emphasize resource allocation directly. 5. Decision Analysis _______________________________ c _ No capability to simulate alternatives. 6. Forecasting________ Very good for indicating whether or not schedules can be met. 7. Updating_______________________________________ _ Considerable clerical effort needed to update graphs. Computer processing can reduce this effort. 8. Flexibility ______________________________________ _ Inflexible. When major program changes occur, all LOB phases must be redesigned. 9. Cost______________ Data gathering and computations can be handled routinely and at moderate expense. Pam 1-54 CHAPTER 4 NETWORKING TECHNIQUES The network is a composit~ refinement of a number of the charting techniques that were presented in chapter 2. The network and related techniques have proven to be very effective control devices for complex one-of-a-kind projects. These techniques have been especially effective for large development and construction projects. Since older scheduling 'techniques have never enjoyed much success in connection with these kinds of projects, networking is considered an important advance in project management. In order to construct a complex network it is usually advantageous to prepare what is known as a work breakdown structure. In this section the work breakdown structure will be described first,· followed by discussion of the network, time estimating, critical paths, scheduling and manpower loading, network families, and evaluation of networking. The numerous computer programs available for processing networkrelated data are not discussed. Information on computerized networking may be found in most of the references on networking identified in the bibliography. 4-1. Work Breakdown Structure As in other management endeavors, the first step in developing a network is establishing goals: The major goal and each supporting goal for the entire project. "When these goals have been identified they must be linked together so that the planner c.:m see the relationships among all the steps of the project. In simple projects, the major and supporting goals are easily and quickly seen. For instance, in constructing a small building the contractor can readily visualize the major goal, completion of the building on time. Through experience with similar designs He knows the supporting goals or steps and how they are interrelated. (There are probably 15 to 20 such steps, beginning with site clearing and ending with landscaping.) The contractor, if he were fammar with networking, could quickly and easily construct a network relating each of the goals. In more complex projects, however, such as construction of campus and buildings for a new college, the many hundreds of individuals steps are not so easy to comprehend and relate in one's mind as those in the simple building construction example. Therefore, for complex projects it is common to prepare a work breakdown structure, which pictorially represents the entire program, before attempting to construct the network. The work breakdown structure diagrams the way that supporting goals mesh together to attain the major goal. Ithelps the planner to identify the goals and to get a total picture of the project, though not in complete detail. The work breakdown structure is illustrated in figure 4-1 using the missile system example. It begins with the major goal, in this case the completed "missile system." This goes on the top or first level of the work breakdown structure. The second level contains supporting goals and each succeeding level shows more detailed tasks to support each of the goals in the level above. Because of space limitations, only "missile" at the second level is broken down Pam 1-54 WORK BREAKDOWN STRUCTURE Level 1-MISSILE SYSTEM II I I I INSTALLATION GROUND OPERATING TRANS- 2-IIISSIL£ 8CH£CKOUT £0UIPII£NT PERSONNEl £0UIPII£NT PORTAT/ON .... _ II ,.. .. I PROPULSION REENTRY BAlliSTIC 3- ENGIN£ VEHIClE SHEll I J .. I I NOS£ £0UIPII£NT 4-BODY FAIRING SECTION I ... A I y I IIISSIL£ POWER INSTRU- 5-SECTION CABlE ASSEMBLY 11£NTATION ASS£1/BLY Figure 4-1. into lower level tasks, and only a few of the lower level tasks are shown. All the other lower level blocks would be shown and broken down the same way in actual practice. How many levels should 'the work breakdown structure have~ This depends on the number levels of management that the networks and schedules are being prepared for. Thus, if we are concerned only with scheduling and controlling at top and second levels of management, a two-level work breakdown structure is sufficient. In a project as complex as this, however, networking would greatly aid in control for several levels, and a finer work breakdown structure would be needed. The level of detail on a work breakdown structure should be extended until . "managealble" end products have been defined. The five levels shown in figure 4-1 provide the basis for networks for five levels of management. It will be seen in later discussion that activities lists in more detail than those in table 1-1 would be required to actually construct networks for these lower levels of management. Requirements for cost information, for example, should be compatible with DOD Instruction 7041.2 which specifies the level of structuring required. The activities in table 1-1 support only the secondlevel blocks of the work breakdown structure. Though the work breakdown structure resembles an organization chart, the blocks must not be thought of as organizations. The work breakdown structure ·Pam 1-54 is product oriented, and the blocks will rarely correspond to the organization ( s) responsible for the tasks. The work breakdown structure also should not be considered to be entirely an end item 'breakdown, for it contains hdth end items, "products," and services such as transportation. 4-2. Network a. In this discussion the progression from the work breakdown structure to an activities list to network construction will be presented. But first 'the simple concepts underlying the network will be discussed : ( 1) An activity (or task) is depicted by an arrow: ( 2) A sequence of activities is indicated by linking arrows : --------~·~() ~ (3) There is an activity description for each arrow. Activity descriptions may be related to arrows through coded lists or wriitten directly adjacent to the arrow on the network diagram: ACTIVITIES LIST A. Develop Engine B. Develop Shell PEYELOP £1&11£ NETWORK DIAGRAM (4) An event occurs at a point in time and signifies start or completion of an adtivity. The events link activities and are represented by geometric figures (e.g., a circle). Events may be coded and identified on separate event lists: NETWORK DIAGRAM EVENT LIST -1. Engine Developed Pam 1-54 Event descriptions normally are written in the past tense to represent completions. This contrasts with activity descriptions, which are in the present tense (imperative mood) to represent work being performed. Thus, "develop engine," the activity description above, is easily changed to the event description, "engine developed." Similarly all of the activity descriptions in table 1-1 could be written as event descriptions; e.g., "operating personnel trained" inStead of "train operating personnel." (Event numbers rather than activity numbers would then be required. Since the activity number is 1-2, the event number, signifying completion, would be 2.) (5) A grouping of activities and events forms a network. Networks may be either activity-oriented or event-oriented. In activity-oriented networks the activities (arrows) are labeled; in event-oriented networks the events (e.g., circles) are la,beled. The following network is eventoriented: Event List 1. Start 2. Walls torn out 3. Plumbing installed 4. Wiring installed 5. Carpentry completed 6. Inspection completed There are certain rules to follow in constructing a network; e.g., no looping is allowed : INCORRECT This loop shows that event 1 must be completed before event 2, event 2 before event 3, and also event 3 before event 1. This "vicious circle" of precedences obviously is not logically possible. Pam 1-54 Another rule of network construction is that only one arrow (activity) can connect two events. Instead a dunrm;y activi~y is included: INCORRECT CORRECT OR--- In the incorrect version, event 2 would have to stand for completion of two activities, which is confusing (and especially nettlesome to a computer when the process is mechanized). In the correct versions the added· ( dunrmy) event 3 signifies completion of one of the activities and event 2shows completion of the other. The dashed dummy activity, 3 to 2, involves no work and no time and is merely there to avoid the ambiguity of the incorrect version. (6) The length of an arrow has no signifieance. It merely shows direction of workflow. b. As an example of how networks are constructed, consider the missile system development example from the project manager's point of view. The first step is constructing the work breakdown structure, which for the project manager is the first two levels of figure 4-1. This work breakdown structure identifies five subordinate products tha;t are needed to complete the missile system. The next step is to identify key activities (or events) involved in producing each of these five subordinate products. By key activities, we mean those activities that the project manager feels he should monitor. The reader will recall that in chapter 2 the control points for the leadtime chart and the milestones in the milestone technique were selected in a similar manner. They are the points that warrant monitoring. Let us assume that the project ma.nager feels he should monitor completions of each of the 18 aOtivities listed in table 1-1. Table 1-1, then, would be the product of the effort by the networking staff and the project manager to identify key activities for e'aOh subordinate goal on the work brealkdown structure. Activity 1-6, "fabricate missile," is a large, complex activity in itself, and perhaps· a project ma.nager would prefer to break it into several milestones, like "fabricate propulsion engine," "fabrica;te reentry .vehicle," and "fabricate ballistic shell" (level3 of fig. 4-1). However, to simplify this example let us assume only these 18 activities. The third step is arranging these 18 activities logically into a network, noting .all obvious precedence constraints and the less obvious ones dictated by Pam 1-54 notes (a) and (b) below table 1-1. Figure 4-2 is the resulting network. There is no other logical way the network can be arranged (though the shape can vary). Activities 2-7 and 3-7 must merge because operating personnel and ground equipment are needed at the site before the operating personnel can install the ground equipment. Note (a) from table 1-1 is also obvious: the missile can't be installed at the site until the installation equipment is at the site. The dummy activity 10-11 is needed in this case to indicate this precedence requirement. It cannot be a solid line, because no work is going on and no time elapses. Activity 12-13 can be analyzed similarly, and the other merge points (5-9 and 6-9, 7-12 and 10-12, and 12-14 and 13-14) are obviously necessary. The event numbers shown in table 1-1 would actually not be assigned until the network is constructed. There is no significance to the numbering arrangement; any numbers (or letters) could be used for any of the events. The left-to-right flow of numbers shown in figure 4-1 is common but by no means necessary. 4-3. Time Estimates Equally as important as the activity interrelationships are the activity times. By knowing how long each activity in a network is likely to take, we can predict how long the total project is likely to run. Time estimating for each activity may be done when preparing the activities lists or after the activities are arranged into a network. In any case the estimates should be made by the best available authorities with the assumption of normal conditions. For example, the transportation foreman or dispatcher is likely to know best how long it will take to carry out each of the four transportation activities. His estimate should be solicited. A word of caution, however. Those experienced in many kinds of scheduling techniques have noted a common tendency of line managers to overestimate activity completion times. One reason for this tendency is that line managers' time estimates are typically cut by higher authority when scheduling is done, and it thus behooves them to pad their original estimates. Therefore, in networking various ways of correcting for these overestimates are used (e.g., the probabilistic three-time estimating practice that has been used with PERT). Carrying the missile system development example further, time estimates for each 1\ctivity are included in table 1-1 and in figure 4-1. Assume that these estimates are realistic: The authorities doing the estimating were influenced not to pad their estimates, or else their padded estimates were adjusted. The estimates, then, represent the expected activity completion times, assuming normal conditions. 4-4. Critical Path In any network there are various sequences or paths of activities between the initial event and the final event. These paths vary in total time, each being the sum of all the activity times on the path. The path or paths taking the longest time are called critical paths. A critical path may usually be reduced by devoting more resources to the activities on the path, thus shortening the entire project. Of course, as one critical path is shortened, another eventually becomes critical. Paths in a network that are not critical have what is called slack (or float) time. For example, in a simple two-path network, if the critical path is 10 weeks long and the other path 6 weeks long, the other path would have 4 weeks of slack (10-6=4). This simply means that one of the activities on the slack path rliSS"ILE S""..,S"TErl DIE_~~ELOPrlENT NET,a ~oRK I TRAHSI¥JIT IJP£RAT/NG P£1SONN£L TO SIT£ I 51T£ ra~•s'o~~u,,•r•r ro ,aou•D I I 7 TIAISPOIT TIAISFEIIESPOIS/1/l/Tf r ........... ·-..........--..... JJ ( 4 ) T£STIISTALLATIO¥JJ IISTALLAT/011 • ( ~ !IIDPfiAT/IIAl (15 0 I CNF&IOUUQUIP/17. CN£&10UT£0UIPI'l 111/TTO TO SIT£ IISIIG &OIIAI8 TIAISPOIT '*ISSIJ£ 011/SS/1.£ TIAIS .,. ~~·· I'PITAT/11 Y£8/&l£ a 3 TOSIT£ t Figure 4-2. ..c!,. Pam 1-54 could be delayed 4 \Yeeks without affecting the 10-"-eek completion time for the whole network. Under some· conditioi1s manpmver or other resources can be taken from a slack path and put on critical path tasks to reduce total project time. In the missile system development example the bottom path, activities 1-6-9-11-13-14-15, is 50 weeks long. This is much longer than any of the other six paths (the two paths that include dummy activities 10-11 and 12-13 must be included), and thus the lowei· path, emphasized by broadened lines, is critical. Since early project. completion' is nearly always a management goal, there would probably be an attempt to pour more resources into one or more of the six activities on the critical path and thereby shorten the project. At this point it is worthwhile to note the contrast between the network and the simple charting tec;hniques in figures 2-2, 2-3, and 2-4 of chapter 2. These figures show the same 50-week duration for the total missile system project. Furthermore, the same critical path activities adding up to 50 weeks can be identified in the figures. The main "-eakness of the Gantt chart for complex projects can nmY be readily seen: It doesn't show precedence (sequential) activity relationships. The leadtime chart does show these relationships, and in addition it has the advantage of a time scale so that lengths of Jines visually correspond to time. HoweYer, it has a weakness in that short but important activities, like the transportation activities, may be 'too short to show up at all and must be combined with other activities. Also, the time scale feature complicates chart construction and may be almost impossible for very complex projects. For this and other reasons, the network has been preferred for most complex one-of-a-kind projects. 4-5. Scheduling and Manpower Loading The above paragraph pointed out the Yalue of the network in showing clearly the necessary sequences of activities. Earlier paragraphs showed how activity times rnay be added along each path to giYe management valuable time data for use in making resource allocation decisions. But for the actual time scheduling of network activities, the Gantt chart is still recommended. The Gantt chart has the needed time scale, which may be calendar dated, and the schedules as plotted on Gantt charts are most suitable for use by line managers in directing \York performance. In entering the actiYiti<:>s on the Gantt schednle charts, hmYever, there are alternatives for activities not. on the ('J"itical path. If there are 5 weeks of slack on a slack path, for example~ this means there are :) weeks leeway as to the scheduled start time for one or more activities on the path. ShouM all activities be scheduled to start at. the earliest possible time? This is normn.lly good policy since activities may take longer than expected. An exception to this policy occurs when common manpower is used for a number of activities on a nehYork. and the manpower is limited. Assume, for example, that 50 machinists are available to 'York on the four actiYities sho\vn in (a), figure 4-3, and that their skills are interchangeable; (a), figure 4-3 shows how many of those :)0 men are needed on each activity and for how many \Yeeks (estimated). It can easily he seen that ncti,-ities 1-2 and 1-3 together would take 55 men, 5 too rnany. Thus, they cannot both be scheduled in week 1; (b), figure 4-3 shows this impossible schedule, and it shows further that activity 2-5, when scheduled at its earliest possible time (after completion of activity 1-2), would begin at the same time as activity 2-3. This is an overload of 11 Pam 1-54 NETWORK ·sCHEDULE and MANPOWER LOAD Network (a) Original Schedule (b) tiiTitAL J------:-::------.---:--:--.-----------y--------1 PATH t-----=----....L--=-::--L-----:-::-----.l---...:._.:....___ _.J 5 Manpower Loading (c) •• ••••••••••••••••••• •CAPACITY WEEk wrn Figure 4-3. men (38 +23-50) in weeks 5 and 6 and overload of 13 men (40 +23-50) in week 7. The shaded extensions of bars 1-iJ and 2-5 show the available slack for these activities. To avoid these numpo,Yer overloads in week 1 and in weeks 5, 6 and 7, the procedure is to move bars 1-3 and 2-5 ch;ewherc within their slack zones to points where there is no overloading. Ifthis isn~t possible, more manpower must be found, or the project schedule must be extended. In this example, however, it is possible: Move activity 2-5 to weeks 11, 12 and 13; move activity 1-3 to week 5. Pam 1-54 Figure 4-3, (c) shows the manpower load diagram for the original impossible schedule and for the adjusted schedule. 4-6. "Crashing" the Network (Time-Cost Function) An obvious advantage of the network orer other program display devices is that the network shows which activities are the bottleneck activities; i.e., those on the critical path. Thus, to shorten or "crash" a tqtal project it is necessary only to speed up activities on the critical path. 'iVithout knowledge of critical-path activities a ·project manager would simply crash all activities, critical and slack, greatly wasting resources. But though the network identifies the critical path that should be crashed, the project manager must still decide which of the critical path activities should receive most attention. A useful aid in making this decision is the simple timecost tradeoff technique. It requires four estimates for each critical-path activity: (1) Expected normal activity time: (2) normal activity costs; (3) reduced activity time if the activity were crashed; and (4) cost on a crash basis. These estimates are based on the principle of the time-cost curve, as illustrated in figure 4-4. In this example, the normal activity time estimate is 6 weeks and the normal cost estimate is $10,000. On a crash basis, the activity time is reduced to 4 weeks and the cost increased to $20,000. The simple assumption is that cost increase is linear with decreases in time. For example, shortening the time by half a week increases cost by $2,500; by a whole week, $5,000; by a week and a half, $7,500. All these points would fall on the straight line in figure 4-4; thus the linear assumption. For this example it can be seen that the added-cost to decrease the time is $1,000 per day decreased. This time-cost tradeoff procedure should be carried out for each activity on the critical path. It will sometimes be found that an activity cannot be reduced for any amount of money-machine-controlled processes are in this category. TIME-COST TRADE-OFF COST (Thousands ofDollars) &IASI 2..... '"' ~ "~$ lJ I".., IIIlA ~ T I 2 .; 4 5 6 7 8 9 10 TIME (Weeks) Figure 4-4. Pam 1-54 But through use of overtime, extra shifts, expediting deliveries, and various shol'Wuts, many activities can be reduced in time-at a price. The activities that can be reduced for the least additional cost should be crashed first. (The activity represented by figure 4-4 costs $5,000 per week reduced; if other activities on the critical path cost more per 'veek, extra resources should be poured into this activity first.) 4-7. Network Families The fact that various levels of management and numerous interrelationships among firms, agencies, and military offices are involved in materiel acquisition was brought out in chapter 1 of this pamphlet. In such an environment with its variety of demands a single network often will not suffice. Therefore, it is common for several different levels of management and each of the various agencies and contractors to have their own network for managing their own aspects of a total project. The entire group of networks can be thought of as a family of networks, all fitting together. This idea was touched on briefly in the earlier discussion of the work breakdown structure: Each level. of the work breakdown structure would have its own networks, varying in amount of detail from level to level. A three-level family of networks is shown in figure 4-5. The five top-level activities are of interest to top management. Second-level managers would want the greater detail shown in the second-level detail network. Because of space limitations only one pair of events, 7-8, on the detail network is broken down further into a subnetwork. The third-level manager concerned with activity 7-8 would use this subnetwork. Pam 1-54 NETWORK FAMILY Sub-Net Figure 4-5. Sometimes it is desirable to break up a network into several pieces for different managers involved-a sort of horizontal ncbYork family. For example, each of the second-level managers concerned with the detail network in figure 4-5 might want a network shoiving only his own activities. However, caution must be exercised in bren.king up a network: Interfacing events-those events that are common to more than one manager--can pose special problems. Pam 1-54 This can be demonstrated by extracting from the missile system network of figure 4-2 only those activities of concern to the manager of operating personnel: Activities 1-2, 2-7, 7-12, 12-14, and 13-14. These activities placed in a separate network would look like this : · The complication is those extraneoues arrows identified as 11, I2, and l 3• They signify interfacing activities, performed by contractors and other inhouse managers, that must be completed before the next activities (7-12, 12-14, and 13-14, respectively) can begin. The point of this is that if a network is split up, interfacing activities (or events) must be identified. An individual manager cannot go his merry way independently when his activities interface with those of other managers. The managers must keep abreast of one another's progress to maintain realistic control of their own activities. 4-8. Evaluation of Networking The network simply and explicitly displays interrelated events. It therefore has great value as a communication device. It provides a common framework :for discussion for different levels of management. Since time estimates lead to identifying a critical path, management can focus attention on the activities on the path. Extra resources may be applied to these activities, perhaps by reallocation from activities on slack paths. This focus on the critical path, however, may obscure the fact that a second path may be very nearly critical and would become critical with slight delays. Therefore, the second most critical path, third most critical path, etc., should be identified and given appropriate attention. The time-cost function is a powerful tool for introducing the important cost element into the business of time scheduling, which too often tends to emphasize only time considerations. The uncertainties of time-estimating for complex projects, especially development projects, cannot be onrcome by networking or any other technique. It must simply be recognized that estimates will not be accurate. Howe;ver, attention should be paid to the tendency of line managers to pad estimates. Also, it should be recognized that estimates when obtained are not inviolable. They should be constantly modified as new information sheds more light on expecte,d times to complete activities. Table 4-1 summarizes strengths and weaknesses of networking. Pam 1-54 Table 4-1. Networking-Strengths and Weaknesses Criteria Strengths 1. Accuracy_______________________________________ _ 2. Reliability____________________ -----_ -______ ----__ 3. Simplicity________ Brings simple order out of mass confusion. 4. Universality of Very good for one-time pro Project Coverage. grams like construction and development projects. 5. Decision Analysis__ Excellent for simulating alternatives, especially when coupled with time-cost data. 6. Forecasting______ _ Excellent for forecasting ability to meet schedules. 7. Updating________ _ Easy to update estimates as progress information is received. 8. Flexibility_______ _ Portions of network can be easily changed to reflect program changes. 9. Cost____________________________________________ Weaknesses The technique is as accurate as the activity time estimates. The margin of error is generally less in construction than in development. Compounded unreliable estimates in a large project may lead to unreliable status information. Concepts of slack and network families sometimes difficult to grasp. Computerized networking vastly complicates the process. Weak in production phase of life cycle. Not well-suited for quantity production. Since considerable data is required, it is usually costlyespecially if computerized. Pam 1-54 CHAPTER 5 OTHER SCHEDULING CONSIDERATIONS 5-1. Manpower Capacities vs. Manpower Requirements In scheduling work for organizations (shops, cost centers, departments, etc.) the manpower capacity of the organization must be matched against manpower required for the jobs to be scheduled. That is, we must make sure that the availruble manpower is in line with the manpower needed. This comparison is made for all the jobs to be scheduled in a given time period. The time period may be a week, a month, etc. The manpower required is simply the sum of the stand·ard times (engineered time standard or best estimate) for each job to be done in that period. For repetitive production, the standard time for one unit is multiplied by the units to be produced in the period. The result is standard hours of work to be done in the period. The manpower capacity of the organization is not just the number of employees on the rolls. The net capacity must allow for employees on leiave (all kinds of leave) plus two other factors, commonly called u