Pert Charts

Trisha Cummings

What Are Pert Charts?

 "PERT" developed by the United States Department of Defense as a management tool for complex military projects is an acronym for "Program Evaluation and Review Technique".  Pert charts are used for project scheduling

 Pert charts allow software planners, or individuals to:  Determine the critical path a project must follow.  Establish most likely time estimates for individual task by applying statistical models.  Calculate boundary times that define a time ‘window’ for a particular task.

How To Create A Pert Chart?

        Make a list of the project tasks. Assign a task identification letter to each task. Determine the duration time for each task. Draw the PERT network, number each node, label each task with its task identification letter, connect each node from start to finish, and put each task's duration on the network. Determine the need for any dummy tasks. Determine the earliest completion time for each task node. Determine the latest completion time for each task node. Verify the PERT network for correctness.

 Slack time is calculated for each node by subtracting ECT for a node from its LCT. Critical path is any node that has zero slack time.  Formulas:  O = Optimistic time estimate  M = Most likely time estimate  P = Pessimistic time estimate

Advantages of Using Pert Charts.

  PERT charts can become very complex if detailed networks exist, but they force the manager to contemplate personnel assignments for the project in detail. To demonstrate best- and worst-case project scenarios, most PERT charts identify three time estimates: most optimistic, most pessimistic, and most realistic. PERT charts are very useful in large, complex studies where overlooking details may create unresolvable problems. PERT charts are frequently used within an organization for detailed evaluation planning. The Critical Path of a PERT chart highlights important interim deadlines that must be met if the overall evaluation study is to be completed on time.

PERT strengths

 The PERT network is continuously useful to project managers prior to and during a project. The PERT network is straightforward in its concept and is supported by software. The PERT network's graphical representation of the projects tasks help to show the task interrelationships. The PERT network's ability to highlight the project's critical path and task slack time allows the project manager to focus more attention on the critical aspects of the project-time, costs and people. The project management software that creates the PERT network usually provides excellent project tracking documentation. The use of the PERT network is applicable in a wide variety of projects.

PERT weaknesses

 In order for the PERT network to be useful, project tasks have to be clearly defined as well as their relationships to each other. The PERT network does not deal very well with task overlap. PERT assumes the following tasks begin after their preceding task end. The PERT network is only as good as the time estimates that are entered by the project manager. By design, the project manager will normally focus more attention on the critical path tasks than other tasks, which could be problematic for near-critical path tasks if overlooked.

PERT Chart showing Dependency Information

 This PERT chart displays the type of dependency directly on the dependency line itself. Also notice that the Start-to-Start and Finish-to-Finish dependencies connect to the left and right edges of the PERT boxes. This means that a Start-to-Start (SS) dependency will come from the left edge of a box into the left edge of the other box.

References

 http://www.cse.fau.edu/~maria/COURSES/CE N4010-SE/C8/PertCharts.htm