20-07-2013, 03:11 PM
Client Packet: Project Managment
Client Packet.doc (Size: 472.5 KB / Downloads: 52)
What is PERT / CPM?
PERT (Program Evaluation and Review Technique) is a logical method for organizing the "on-time, on‑budget" completion of projects that was originally developed by the Navy in 1958 to manage the Polaris missile project. CPM (Critical Path Method) is a very similar technique that was developed by the RAND Corporation1 in 1957 (and likely 'borrowed' by the Navy). There is not really any major logical difference between PERT and CPM, and most people today consider them to be the same technique. [However, some academics still refer to them as two different techniques since they do have some minor technical differences.] PERT is also logically similar to certain other planning techniques, ie, Gantt Charts and Material Requirements Planning (MRP) as well; the similarity that is easiest to observe is that, in a sense, all three techniques count backwards from the desired finish time to plan task start times.
Constructing A PERT / CPM Diagram
Paradise Resort management has hired the Windward Pool Company to install an Olympic-sized pool on their grounds. From past experience, both Paradise Resort and Windward management knows what the major tasks are that must be completed during the project, as well as how long each task takes.
"Backward" Calculating the Critical Path
So far, Paradise Resort has a easy-to-read diagram that shows the order in which the tasks will be done, as well as the minimum project finish time (12 days). Not every task has to stay "on schedule," however, in order for Windward to finish the entire pool project on Day 12. For example, look at Task F. It is supposed to start on Day 2, but it's easy to see that if, for some reason, it started as late as Day 4, the entire pool project would still finish "on schedule" on Day 12. Of greater concern is which tasks do NOT have "extra time;" ie, must start and finish as scheduled in order for the entire pool project to finish "on schedule." These tasks can be identified by completing a backward calculation, ie, counting up the days required from right to left along the various paths. The results of this "backward counting" is usually noted along "the bottoms" of the tasks. The forward calculation determined a schedule based on every task starting "as soon as possible;" eg, Task F can start as early as Day 2 (if all goes well with Task E). The backward calculation, however, will determine a schedule based on every task finishing "just-in-time" (or "at the last minute);" eg, Task F could start as late as Day 4 without making the entire pool project late. Start by placing a 12 the lower right‑hand corners of Task D and Task F; if Task D OR Task F finish any later than that, the entire pool project will be late.
Time / Cost Trade-Offs (or Project Crashing)
Paradise Resort management now knows that the Windward Pool project takes no less than 12 days. Unfortunately, Paradise Resort advertised that their new pool would be available during the "in‑season," just 11 days away. The Windward project can be started right away, but Paradise would be willing to pay extra to speed up ("crash") the project by one day, if possible. Windward quickly puts together the following table of information.