How to Construct a Pert Chart
Program Evaluation and Review Technique (PERT) charts were created in the late 1950s for the U.S. Navy. The strength of the PERT chart is that the system of organization allows for unknown variables while still presenting a concrete workflow. This type of technique can be especially effective when dealing with large projects with involving employees in different locations. Charts are divided into activities and events: activities representing jobs that must be performed, and events representing a significant step. PERT charts can be helpful in anticipating completion times of large projects, as well as how much a delay in a particular activity will impact the completion date.
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Instructions
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Plan activities and sequence. The first step in the creation of a PERT chart is to figure out the exact tasks that must be accomplished, and in what order. Note activities that can be accomplished simultaneously, or that depend on the completion of others.
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Begin to chart nodes. Nodes can be rectangles or circles and represent events (milestones). Number the nodes to represent time passage, i.e., higher numbers as the milestones progress. Using variables of 10 can be useful in case new milestones need to be added throughout the project and you don't want to redo the whole chart.
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Connect nodes with vectors. Activities that contribute to reaching a milestone are represented by arrows--known as vectors--that link the nodes. Activities that begin simultaneously will be represented by arrows leaving the same node, and multiple activities that contribute to a common milestone will be represented by arrows arriving at the same node. Each vector arrow should include the name of the activity, duration and the names and numbers of people assigned to the activity. The duration of each activity should always be expressed by a constant unit of time, and can include three time estimates: "optimistic time," "most likely time" and "pessimistic time." Using these times, PERT uses an equation to calculate the expected time of completion:
Expected time = (Optimistic + (4 x Most likely) + Pessimistic) / 6
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Manage the critical path. The critical path is the longest path between the start and end nodes, and represents all the tasks that must be accomplished on time for the project to be finished on the assigned date. Some activities can be delayed without effecting the critical path, known as "slack time." To determine the critical path, assign each activity four times: earliest start time, earliest finish, latest start and latest finish. These times can then be used to calculate goal dates.
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References
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