In this paper, presented at the 2010 PMI Global Congress Conference, PMA Consultants’s Dr. Gui Ponce de Leon weighs the advantages and disadvantages between CPM and GPM’s use as an analytical tool in Forensic Schedule Analysis to demonstrate how GPM solves the CPM forensic void.
The critical path method (CPM) is widely used as a project management tool. Basic to CPM is for the planner to draw a project network first, and then to use CPM software to calculate activity dates and total floats, establish the project completion date and locate the critical path. Alas, all is not well in CPM utopia! The moment the planner takes control of activity dates by using constraint dates or resource leveling, total float is reduced (some would say sequestered); and once actual dates are introduced in a CPM network, the analyst loses total floats and the critical path can no longer be calculated left of the data date. The ability to schedule an activity later than its early dates without sacrificing total float, and to determine total floats and the critical path for the as-built portion of a schedule (left of the data date), is solved by the graphical path method (GPM). This paper describes the float aspects of GPM, while emphasizing the concept of GPM forensic total float and its role in retrospective schedule analysis, whether in updating or forensic scheduling. A compendium of CPM and GPM float concepts is provided for historical context.