Then each job is drawn on the graph as a circle, with its identifying symbol and time appearing within the circle. Technological ordering is impossible if a cycle error exists in the job data (e.g., job a precedes b, b precedes c, and c precedes a). For convenience in graphing, and as a check on certain kinds of data errors, the jobs may be arranged in “technological order,” which means that no job appears on the list until all of its predecessors have been listed. Nevertheless, the project graph is valuable as a means of depicting, visually and clearly, the complex of jobs in a project and their interrelations.įirst of all, each job necessary for the completion of a project is listed with a unique identifying symbol (such as a letter or number), the time required to complete the job, and its immediate prerequisite jobs. The graph is not an essential part of CPM computer programs have been written which permit necessary calculations to be made without reference to a graph. The concept of CPM is quite simple and may best be illustrated in terms of a project graph. (For example, the foundation of a house must be constructed before the walls are erected.) What is the Method? (3) The jobs are ordered-that is, they must be performed in technological sequence. (This requirement eliminates continuous-flow process activities, such as oil refining, where “jobs” or operations necessarily follow one after another with essentially no slack.) (2) The jobs may be started and stopped independently of each other, within a given sequence. (1) The project consists of a well-defined collection of jobs (or activities) which, when completed, mark the end of the project.
The manufacture and assembly of a large generator (or other job-lot operations).Įach of these projects has several characteristics that are essential for analysis by CPM:.Scheduling ship construction and repairs.Research and engineering design projects.
The construction of a building (or a highway).Widely diverse kinds of projects lend themselves to analysis by CPM, as is suggested in the following list of applications: In essence, the tool provides a means of determining (2) which jobs or activities, of the many that comprise a project, are “critical” in their effect on total project time, and (2) how best to schedule all jobs in the project in order to meet a target date at minimum cost. Recently added to the growing assortment of quantitative tools for business decision making is the Critical Path Method-a powerful but basically simple technique for analyzing, planning, and scheduling large, complex projects.