Five Things You Didn’t Know About the PERT Chart

The Program Evaluation and Review Technique, or PERT, chart is a scheduling tool commonly used in project management to illustrate the dependencies and flow of project events and milestones. For more details about the background and development of the PERT Chart, take a look at Eric Stallsworth’s article, What is a PERT Chart?

Many know how to create and use PERT charts, but how many are aware of the history behind this project management tool and its relationship with other scheduling concepts?

Facts About the PERT Chart

• Also known as a network diagram, the PERT chart was first used in the late 1950s by the U.S. Navy while working on the Polaris missile project during the Cold War era.

• Although Gantt charts and PERT charts are often used hand-in-hand, the Gantt chart actually predates the PERT chart by almost 40 years. However, despite being used earlier, the Gantt chart did become quite a bit more popular during the 1950s, at about the same time the first PERT charts were implemented.

• The tradition of numbering the events in sequences of 10s (or 100s for larger projects) in an initial PERT chart is analogous to the method used by BASIC programmers when assigning line numbers to command statements. In both cases, gaps in the numbering system are intentionally left so that additional items can be inserted at a later date, if needed, without having to renumber the entire project.

• While both PERT and Critical Path Method came into existence at about the same time, the two methodologies were actually developed independently of one another. Check out The History of Project Management: Late 20 Century Process and Improvements by Joe Taylor Jr. for a more in-depth look at the parallel development of these two concepts.

• The PERT chart was the inspiration for the creation of several other scheduling concepts including, but not limited to, MAPS, TOPS, PEP, and PAR. While many of these methods never gained widespread usage, PERT, along with the Critical Path Method (CPM), became standards in the project management world by the end of the 1960s. More information on these other methods can be found in Mosaic’s, A Brief History of Scheduling.