Technical Terms Used in C.P.M [Critical Path Method]
The following technical terms need be understood clearly before constructing the CPM network
An activity is a part of the project denoted by an arrow on the network. The tail of the arrow indicates the start of the activity whereas the head indicates the end of the activity. One and only one arrow is used to represent one activity of given duration. The arrows of the activities are not drawn to scale. The durations of the activities are written along their arrows.
2. Dummy Activity
The activity which neither uses any resources nor any time for its completion is called dummy activity. It is represented by a dotted arrow or a solid arrow with zero time duration.
Event is the stage or point where all previous jobs merging in it are completed and the jobs bursting out are still to be completed. Event 1 is the starting point of the project.
See the figure shown below, where, event 6 is the point where activities B(3), F(3), H(2) and K(5) merge and activity L(4) bursts.
Events are generally represented by circles or nodes at the junctions of arrows. Events are serially numbered in their sequential order.
The diagrammatic representation of the activities of the entire project is called network of flow diagram. On this diagram various jobs of the project are shown in the order in which these are required to be performed.
5. Early Start Time (E.S.T.)
The earliest possible time at which an activity may start, is called early start time.
6. Early Finish Time (E.F.T.)
The sum of the earliest start time of an activity and the time required for its completion is called early finish time.
7. Late Start Time (L.S.T.)
The latest possible time at which an activity may start without delaying the date of the project, is called late start time.
8. Late Finish Time (L.F.T.)
The sum of the late start time of an activity and the time required for its completion is called late finish time.
9. Total Float
The difference between the maximum time allowed for an activity and its estimated duration is called total float. It is the duration of time by which the activity can be started late, without disturbing the project schedule. It is generally denoted by S.
10. Free Float
The duration of time by which the completion time of an activity can be delayed without affecting the start of succeeding activities is called free float. It is generally denoted by S.F.
11. Critical Activities
The event which has no float, are called critical activities. The critical events are required to be completed on schedule.
12. Critical Path
The path in the network joining the critical events is called the critical path of the work.