Manual for Development Projects - Planning Commission

Chapter-7
activities consume time and other organizational resources. Activities are represented by arrows.
We will read the above network in the following way:-
(a) The five circles represent the five events, namely event Nos. 1,2,3,4 and 5.
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(b) The five arrows represent the five activities, namely: activity (1-2); activity (2-4); activity (1-3);
activity (3-4) and activity (4-5). Note that each activity is between two events, namely, the starting event
and the ending event. In case of activity (1-2), the starting event is event No. 1 and the ending event is
event No. 2. In case of activity (2-4), the starting event (which is the ending event of activity 1-2) is event
No. 2 and the ending event is event No. 4. Also note that events are represented by single numbers (i.e.
event No. 1) while activities are represented by two numbers (i.e. activity No. 1-2).
(c) The numbers beside the arrows represent the duration of activities. It could be in days, weeks, or even
months.
(d) The network indicates that before activity (2-4) could start, activity (1-2) should have been completed.
In other words, activity (2-4) is "constrained" by activity (1-2). This is also true in case of activity (3-4)
and activity (1-3). The network also indicates that activity (4-5) is constrained by the completion of both
activity (2-4) and activity (3-4).
(e The network tells us that activities (1-2) and (1-3) can be done simultaneously. In other words, these
activities are not "constraints" to one another. This is also true in case of activities (2-4) and (3-4).
(f) By tracing all arrows leading to the terminal event (event No. 5), we discover that there are two
"paths". One path is through activities (1-2), (2-4) and (4-5) and the second path through activities (1-3),
(3-4) and (4-5). Assuming that the time duration is in days, the first path will take 29 days (10+11+08)
and the second one would take about 36 days (12+16+08).
(g) The "critical path" is the path that has the longest total duration. In our network, the critical path is
that one that would take about 36 days. Consequently, activities (1-3), (3-4) and (4-5) are "Critical
Activities". The critical path total duration corresponds to the completion time of the whole project. In
our network, the project is expected to be completed in 36 days. A sample of PERT/CPM Chart is
enclosed at Annexure-XIX.
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9/23/2010