CPM uses activity oriented network which consist of a number of well recognized jobs, tasks or activities. Each task/activity is represented by arrow and the activities are joined together by events. CPM is generally used for simple, repetitive types of projects for which the activities time & costs are certainly and precisely known. Projects like construction of a building, road, bridge, physical verification of store can be handled by CPM. Thus it is Deterministic rather than Probabilistic model.
Steps in CPM technique:
Step 1: Specify the individual activities
A listing of all the activities in the project is made from the WBS (work breakdown structure).
Step 2: Determine the sequence of those activities
Some activities depend on others for their completion. They need to be identified.
Step 3: Draw a Network diagram
Once the activities & their sequencing have been defined the CPM diagram can be drawn.
Step 4: Estimate the completion time for each Activity
For each activity the completion time need to be estimated. This can be done on the basis of past experience.
Step 5: Identify the Critical path
The critical path is the longest duration path through the network where no activity is slack. The critical path can be identified by determining the following four parameters for each activity:
(a) Earliest start time (ES) – Earliest time at which the activity can start given that its previous activities must be completed first.
(b) Earliest finish time (EF) – It is equal to the earliest start time for the activity plus the time required to complete the activity.
(c) Latest finish time – The latest time at which the activity can be completed without delaying the project.
(d) Latest start time – It is equal to the latest finish time minus the time required to complete the activity.
Advantages of CPM:
(1) The activities & their outcomes can be shown as a network.
(2) It displays dependencies to help scheduling.
(3) It determines slack time.
(4) It evaluates which activities can run parallel to each other.
(5) It determines the project duration which optimizes both direct & indirect costs.
(6) If properly developed & applied CPM can encourage a team feeling.
(7) They are useful in new project managers.
(8) It is widely used in industry.
Disadvantage of CPM:
(1) The critical path is not always clear & needs to be calculated carefully.
(2) Estimating the completion of an activity can be difficult.
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