PERT stands for program evaluation and review technique, and a PERT chart is a PROJECT MANAGEMENT tool used to schedule, organize, and coordinate tasks within a project. The methodology was developed by the U.S. Navy in the 1950s to manage the Polaris submarine missile program. Employing what is referred to as a time-event network, PERT is similar to the CRITICAL PATH METHOD technique, which developed in the private sector at about the same time that PERT was developed. The advantages of using a PERT diagram include the following.
• PERT charts force managers to contemplate personnel assignment for a project in detail, which can be complex but helpful if detailed networks exist.
• 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 useful in large, complex studies where overlooking details may create irresolvable problems.
• PERT charts are frequently used for detailed evaluation planning.
• The critical path of a PERT chart highlights important interim deadlines that must be met if the overall project is to be completed on time.
In a complex production process, such as automobile manufacturing, PERT charts incorporate a variety of terms and symbols, including event nodes, job activity, immediate predecessors, immediate successors, initial and terminal nodes, duration, earliest start time, earliest finish time, and latest finish time.
• Event node is the beginning and the finish of a job, and each is the connecting point to another job. Each event node has a unique number for ease of reference.
• Job activity is the task that requires a length of time for completion. The event-node numbers that mark its beginning and end refers to each job activity. For example, Job 1, 2 is the task between event numbers 1 and 2.
• The immediate predecessor is a job that must be completed before another job can begin. For example Job 1, 2 is an immediate predecessor for both Jobs 2, 3 and Job 2, 4.
• The immediate successor is a job that cannot be started until another job is finished. For example, Job 3, 5 and Job 4, 6 are immediate successors to Job 1, 2.
• Initial and terminal nodes refer to which nodes start a job and which nodes end a job. For example, node 1 is the initial node for Job 1, 2 and node 2 is the terminal node in Job 1, 2.
• Duration is the length of time required for the completion of any job.
• The earliest start time (ES) is, given the cumulative duration of all of the predecessor activities, is the earliest any job can start. For example, Job 2, 3 cannot start until Job 1, 2 is completed and Job 1, 2 will take three days. Therefore the ES for Job 2, 3 is three days.
• The earliest finish time (EF) is the shortest amount of time needed to complete the overall project given the duration of each job and the order of immediate predecessor jobs.
• The latest finish time (LF) is, given the job(s) that any job must feed into, the latest that the job in question can finish without delaying the start of the job where two or more paths merge. Finishing any later would result in delays in the overall project schedule.
• The latest start time (LS) is, given the job(s) that any job must feed into, the latest that the job in question can begin without delaying the start of the job where two or more paths converge. Missing this start time would result in delaying the immediate successor’s start.
The major advantage of PERT is that it forces managers to plan their activities.