Critical Path Method

Military Requirements for Chief Petty Officer
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Figure 3-4.-Sample Gantt chart. review technique (PERT) while constructing the Polaris fleet ballistic missile. It focuses on key points and steps that may present potential problems. You will find PERT helpful when scheduling complicated nonrepetitive tasks and as a device to evaluate and report progress. The PERT uses a line chart to show the relationship of tasks and the time required to complete each task. The chart contains lines and nodes (circles) that represent the start and completion of tasks. When using the PERT, you apply a mathe- matical formula instead of guesswork to figure the time needed to perform a task. You need three time estimates to complete the formula. First, estimate an optimistic time (T_O) based on a minimum of difficulties that could occur. Second, estimate a pessimistic time (T_p) based on the maximum difficulties that could occur. Third, estimate a normal completion time (T_n) based on the average time you could expect to complete the task. The formula for figuring estimated PERT time (T_e) is as follows: To construct a PERT network, follow the six basic steps applied to all PERT projects. First, identify the component task you will perform. Second, define the order in which you need to complete the component task. Third, analyze and estimate the time required to complete each component task and for the entire project. Fourth, find the critical path. The critical path is the longest path from the beginning component task to the ending component task. Fifth, look for ways to improve the project though modifica- tions. Sixth, control the project. See figure 3-5 for a sample PERT chart. Critical Path Method. —The critical path method (CPM) is very similar to the PERT. The major difference is the PERT focuses on time without regard to cost. The CPM focuses on both time and cost. The CPM and PERT have three major differences. First, the CPM only requires a one-time estimate. Second, the CPM includes a cost estimate as well as normal and crisis time estimates. Third, the CPM is based on the assumption that you have at least some experience with the work needed to complete each component task. Elements of Effective Control Control systems such as quality control or inventory control need certain elements to be effective: controlled work activities, timeliness, effectiveness, accuracy, and acceptance. These elements of control influence how the work will be accomplished and how long work will take. 3-9

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