Two organizations were the spawning grounds for the new technology. In 1956, E.I. du Pont de Nemours Co., Wilmington, Del., started studying the application of new techniques to run its mammoth engineering and construction projects. The company’s mathematicians decided that a UNIVAC 1 computer could generate a work schedule if it was fed information for sequence of work and the time needed to perform each task. Working at du Pont’s Newark, Del., complex, the company team was assisted by UNIVAC scientists. Working under James E. Kelley Jr. of Remington Rand Co., which made the UNIVAC computer, and du Pont’s Morgan Walker, they set up the basics of critical path method scheduling for construction projects.

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Aware of the work at du Pont and that weapons development programs typically ran far past their deadlines, the U.S. Navy decided to see if this kind of project management and scheduling techniques could be applied to its Polaris submarine program. By the latter half of 1958, the Navy had developed a network system called performance evaluation and review technique, or PERT. It eventually was applied to other weapons programs. Although it was not identical, it shared many char-acteristics with the du Pont system.

The backbone of the du Pont system was a graphical model of the project using arrows to represent activities in a logic diagram. Other arrows depicted which activities were dependent on other activities being completed.

Activities on the project’s critical path can influence the completion date. In the PERT system, the arrows represented the time between events, not the duration of activities.

Everyone understood that using a computer would not determine exactly what would happen. "They were mere estimates and subject to some tolerance," says Frederick L. Plotnick, a Jenkinstown, Pa.-based scheduling expert and consultant who also is co-author with James J. O’Brien of CPM in Construction Management. "No individual actually thinks that a project will finish on March 27, 2007, at exactly 4 p.m. simply because the CPM calculation prints out that date."

Variations of both CPM and PERT were developed. H.B. Zachry Co., San Antonio, developed a form of CPM called precedence diagramming method, which is widely used today in place of the old activity-on-arrow diagramming method. Organizations such as the U.S. Army Corps of Engineers and the National Aeronautics and Space Administration and other federal agencies soon started using the CPM methods.

When PCs became popular, CPM programs and techniques were available to a large number of people. Regular updates of schedules could be made to reflect new information.


While the essentials of project management remain the same, some changes are foreseen. Some may involve the theoretical underpinning of project scheduling. For example, one team of researchers recently proposed adapting newly developed theories about scheduling constraints to come up with a hybrid system that combines techniques used in manufacturing with CPM and PERT. It would involve identifying and exploiting constraints and eliminating the excess safety time or buffers.

Others believe that future project managers will incorporate CPM schedules into more comprehensive enterprise management systems. "The environment our customers have had to deal with is one of data silos," says Sue Watkins, director of marketing for Meridian Project Systems Inc., Sacramento. She says schedule programs will be integrated with project management, facilities management and other functions.

Another aspect of scheduling, expressing the probability that activities will be completed by a certain date, likely will become more popular as users become more comfortable with the mathematical expressions involved, says Plotnick. Programs such as Primavera’s Monte Carlo allow users to express the probability in words or percentages.

he practice of scheduling projects with the help of mathematics matured just as computing power arrived in the form of massive mainframes in the late 1950s. With PCs now available that are more powerful than the old mainframes, some believe today’s simplified popular scheduling software eventually may be integrated into other business programs or used with more sophisticated add-on features.