Figure 3-4.-Sample Gantt chart.review technique (PERT) while constructing thePolaris fleet ballistic missile. It focuses on keypoints and steps that may present potentialproblems. You will find PERT helpful whenscheduling complicated nonrepetitive tasks and asa device to evaluate and report progress.The PERT uses a line chart to show therelationship of tasks and the time required tocomplete each task. The chart contains lines andnodes (circles) that represent the start andcompletion of tasks.When using the PERT, you apply a mathe-matical formula instead of guesswork to figurethe time needed to perform a task. You need threetime estimates to complete the formula. First,estimate an optimistic time (T_{O}) based on aminimum of difficulties that could occur. Second,estimate a pessimistic time (T_{p}) based on themaximum difficulties that could occur. Third,estimate a normal completion time (T_{n}) based onthe average time you could expect to complete thetask. The formula for figuring estimated PERTtime (T_{e}) is as follows:To construct a PERT network, follow the sixbasic steps applied to all PERT projects. First,identify the component task you will perform.Second, define the order in which you need tocomplete the component task. Third, analyze andestimate the time required to complete eachcomponent task and for the entire project.Fourth, find the critical path. The critical pathis the longest path from the beginning componenttask to the ending component task. Fifth, lookfor ways to improve the project though modifica-tions. Sixth, control the project. See figure 3-5for a sample PERT chart.Critical Path Method. —The critical pathmethod (CPM) is very similar to the PERT. Themajor difference is the PERT focuses on timewithout regard to cost. The CPM focuses on bothtime and cost. The CPM and PERT have threemajor differences. First, the CPM only requiresa one-time estimate. Second, the CPM includesa cost estimate as well as normal and crisis timeestimates. Third, the CPM is based on theassumption that you have at least some experiencewith the work needed to complete each componenttask.Elements of Effective ControlControl systems such as quality control orinventory control need certain elements to beeffective: controlled work activities, timeliness,effectiveness, accuracy, and acceptance. Theseelements of control influence how the work willbe accomplished and how long work will take.3-9