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Pert- program evaluation and review technique


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Pert- program evaluation and review technique

  2. 2. VINCI VIVEKA•A statistical tool, used in project management• It is designed to analyze and represent the tasksinvolved in completing a given project.•A decision making tool designed to save time inachieving end objectives.•It is one of the techniques of scientific management.•It was developed for the U.S. Navy Special ProjectsOffice in 1957 to support the U.S. Navys Polarisnuclear submarine project
  3. 3. PERTPERT chart is a tool that facilitates decision making.PERT is a method to analyze the involved tasks in completinga given project, especially the time needed to complete eachtask and to identify the minimum time needed to complete thetotal project.PERT is valuable to manage where multiple tasks areoccurring simultaneously to reduce idleness.For this it takes into consideration three factors: 1. Time 2. Resources 3. Technical Performance Specifications. VINCI VIVEKA
  4. 4. TERMINOLOGYPERT Event: a point that marks the start or completion of one ormore activities. It consumes no time and uses no resources. When itmarks the completion of one or more tasks, it is not “reached” (doesnot occur) until all of the activities leading to that event have start and finish*Predecessor Event: an event that immediately precedes some otherevent without any other events intervening. An event can havemultiple predecessor events and can be the predecessor of multipleevents. Eg: A and b are predecessor of C*Successor Event: an event that immediately follows some otherevent without any other intervening events. An event can havemultiple successor events and can be the successor of D is the successor of C*.*(refer Gantt Diagram) VINCI VIVEKA
  5. 5. Optimistic Time (O): the minimum possible time required toaccomplish a task, assuming everything proceeds better thanis normally expectedPessimistic Time (P): the maximum possible timerequired to accomplish a task, assuming everything goeswrong (but excluding major catastrophes).Most Likely Time (M): the best estimate of the timerequired to accomplish a task, assuming everything proceedsas normal.Expected Time (TE): the best estimate of the timerequired to accomplish a task, accounting for the fact thatthings dont always proceed as normal (the implication beingthat the expected time is the average time the task wouldrequire if the task were repeated on a number of occasionsover an extended period of time). TE = (O + 4M + P) ÷ 6 VINCI VIVEKA
  6. 6. PERT Activity: the actual performance of a task whichconsumes time and requires resources (such aslabor, materials, space, machinery). It can be understood asrepresenting the time, effort, and resources required to movefrom one event to another. A PERT activity cannot beperformed until the predecessor event has occurred. Eg:A,B,C,D*Float or Slack is a measure of the excess time andresources available to complete a task. It is the amount of timethat a project task can be delayed without causing a delay inany subsequent tasks (free float) or the whole project (totalfloat). Positive slack would indicate ahead of schedule; negativeslack would indicate behind schedule; and zero slack wouldindicate on schedule.Critical Path: the longest possible continuous pathway takenfrom the initial event to the terminal event. It determines thetotal calendar time required for the project; and, therefore, anytime delays along the critical path will delay the reaching of theterminal event by at least the same amount. VINCI VIVEKA
  7. 7. Activity Predecessor Time Estimates Te O M P A - 2 8 6 4.00 B - 3 5 9 5.33 C A,B 4 5 7 5.17 D C 4 6 10 6.13 TE = (O + 4M + P) ÷ 6 VINCI VIVEKA
  8. 8. Gantt Chart( According to the table in previous chart) Activity On Node (AON) Diagram VINCI VIVEKA
  10. 10. In order to determine these following are the steps-EARLY FINISH [ EF ]Formula for EF= ES + Duration.Duration can be taken from the table it is represented by TeFor the first activity i.e. START Early Start [ ES] =0, VINCI VIVEKAAs start is a pert event its duration is zero.Therefore, for STARTES=0 Duration =0 ; EF= ES + Duration => EF=0EF of the predecessor event becomes ES of its successor.Therefore, for AES=0 Duration=4, EF=4For B,( as A&B both have same Predecessor i.e. START hence B----ES=0 Duration= 5.33 EF=5.33For C ( as A&B both are C predecessor hence we take the one with highervalue)ES=5.33 Duration=5.17 EF=10.5
  11. 11. For D,ES= 10.5 Duration=6.13 EF=16.63For FINISH [as FINISH is a pert event its duration is zero]ES=16.63 Duration=0 EF=16.63LATE START [ LS ]Formula LS=LF – DURATIONIn this we start with FINISH, as it is the last activity. LATE FINISH [LF ] ofFINISH = its EF.Therefore, LF=EF=16.63 Duration= 0 LS=LF- Duration , Hence LS=16.63For D, [ LS of successor event becomes LF for its predecessor event ]LF=16.63 Duration=6.13 LS=10.5For C,LF=10.5 Duration=5.17 LS=5.33For B,LF=5.33 Duration=5.33 LS= 0VINCI VIVEKA
  12. 12. For A, [ as C is also its successor ]LF=5.33 Duration=4 LS=1.33For START [as A&B both are successor but we take here one with the lowervalue ]LF=1.33 Duration =0 LS=1.33 VINCI VIVEKASLACKTo determine the critical path we have to find whether any activity has a slack.Activity on the critical path has slack zero.Formula SLACK=LF-EF or SLACK= LS-ESFor START For CLS=1.33 ES=0 SLACK=1.33 LS=5.33 ES=5.33 SLACK=0For A For DLS=1.33 ES=0 SLACK=1.33 LS= 10.5 ES=10.5 SLACK=0For B For FINISHLS=5.33 ES=0 SLACK=5.33 LS=1.33 ES=0 SLACK=1.33
  13. 13. ES=0 DUR=0 EF=0 ES=0 DUR=4 EF=4 START ALS=1.33 SLACK=1.33 LF=1.33 LS=0 SLACK=1.33 LF=5.33ES=0 DUR=5.33 EF=5.33 ES=5.33 DUR=5.17 EF=10.5 B CLS=0 SLACK=5.33 LF=5.33 LS=5.33 SLACK=0 LF=10.5 ES=10.5 DUR=6.13 EF=16.33 ES=16.63 DUR=0 EF=16.63 D FINISH LS=10.5 SLACK=0 LF=16.63 LS=16.63 SLACK=1.33 LF=16.63 VINCI VIVEKA
  14. 14. CRITICAL PATHIt is the longest continous -path way. There can bemore than one critical path or the path can change.In the drawn Gantt diagram there are twoalternatives to reach FINISH and adding thereSLACK timing-START+A+C+D+FINISH=3.99START+B+C+D+FINISH=7.99Hence , the path START+B+C+D+FINISH is thelongest it is the critical path, shown in the diagramin the next slide. VINCI VIVEKA
  15. 15. VINCI VIVEKACRITICAL PATH [ in red ink ]
  16. 16. •PERT chart explicitly defines and makes visibledependencies (precedence relationships) between thework breakdown structure (commonly WBS) elements•PERT facilitates identification of the critical path andmakes this visible•PERT facilitates identification of early start, late start,and slack for each activity•PERT provides for potentially reduced project durationdue to better understanding of dependencies leading toimproved overlapping of activities and tasks wherefeasible.•The large amount of project data can be organized &presented in diagram for use in decision making. VINCI VIVEKA
  17. 17. DISADVANTAGES:•There can be potentially hundreds or thousands of activities andindividual dependency relationships•PERT is not easily scalable for smaller projects•The network charts tend to be large and unwieldy requiringseveral pages to print and requiring special size paper•The lack of a timeframe on most PERT/CPM charts makes itharder to show status although colours can help (e.g., specificcolour for completed nodes)•When the PERT/CPM charts become unwieldy, they are nolonger used to manage the project. VINCI VIVEKA