Look beneath the surface: never let a thing s intrinsic qualities or worth escape you.

Marcus Aurelius, Meditations

The planning methods described so far ignore the influence that limited resources such as capital, labor, and equipment have on project scheduling. They disregard the availability of resources and assume that whenever an activity is scheduled the requisite resources will be on hand. The fact is, necessary resources are not always available, so activities must be scheduled around when they can be obtained. Also, project cost and project duration are interdependent variables. Altering project schedules influences costs, and it is possible to alter schedules to achieve the optimum project-cost, completion date trade-off.

This chapter covers the topics of program evaluation and review technique (PERT), critical path method (CPM), and constrained resource planning methods that enable project managers to assess the impact of time and cost uncertainty on project completion, and to weigh trade-offs between project schedules, costs, and resource utilization. First we look at PERT, which is a way of incorporating uncertainty into schedule estimates, then CPM a similar method except that it explicitly includes cost as a scheduling consideration. We then consider activity scheduling, taking into account the utilization and allocation of limited resources. The chapter ends with a brief discussion of GERT, a method that surmounts some of the problems and limitations of PERT/CPM.