Manual for Development Projects - Planning Commission

Chapter-7
PERT / CPM Techniques
7.13 In many situations managers assume the responsibility for planning, scheduling and controlling
projects that consist of numerous separate jobs or tasks performed by a variety of
departments/individuals. Often these projects are so large and/or complex that the manager cannot
possibly keep all the information pertaining to the plan, schedule and progress of the project in his head.
In these situations, the technique of PERT (Programme Evaluation and Review Technique) and CMP
(Critical path Method) have proved to be extremely valuable in assisting managers in carrying out their
project management activities.
7.14 The US Navy created PERT to plan and control the activities of hundreds of subcontractors who
were building the first US Polarise Missile Submarine. Since many jobs and activities associated with the
Polaris Missile project had never been attempted previously, it was difficult to predict the time to
complete the various jobs or activities. Consequently PERT was developed with the objective of being
able to handle uncertainties in activity completion on time. On the other hand, CPM was developed
primarily for scheduling and controlling industrial projects where job or activity times were considered
known.
7.15 In todays usage, the distinction between PERT and CPM as two separate techniques has largely
disappeared. Modern project planning, scheduling and controlling procedures have essentially combined
the features of PERT and CPM so that a distinction between the two techniques is no longer necessary.
For a project having 5 activities/components, a simple PERT/CPM diagram may have the following
shape:-
Before going into details we should familiarize ourselves with the following terms and symbols:-
i) Network
A systematic diagram showing logical sequences and inter-relationships between events and activities:
ii) Event
The starting point and the ending point of an activity is called an event. Also referred to an "milestone", it
is a statement of accomplished task from there another activity starts. In other words, the starting events
of one activity is actually the ending event of another. This point in time is represented by a circle.
iii) Activity
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Actions taken to accomplish a task are called activities. Unlike events which are merely points in time,
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9/23/2010