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CPA Stage 6 - Identify the CRITICAL PATH

Critical activities are ones that have no free time - they must start and finish when they are planned. There cannot be delays on these activities or the entire project will be late. The critical path is the chain of critical activities which will be found winding its way through the network.

There is a three-point test to see if an activity is critical.

Test 1 - the earliest and latest start times are the same,
Test 2 - the earliest and latest finish times are the same,
Test 3 - start time + duration = finish time (there is no float).

Only if all three tests are met will the activity be critical. Beware of the activity that passes tests 1 and 2 but fails test 3.

Mark the path in some way on the diagram. In figure 8 below, we have marked the path with a series of double lines to make it very clear. In your diagram you only need to mark critical activities with a single set of double lines


Figure 8 Completed network diagram with critical path

Figure 9 gives a reminder of the key to the diagram. If asked to draw one, it is always worth providing a key as well.



Figure 9 Network diagram key

Stage 7 - CHECK IT

So, we now have a plan for our project and know that it should take 18 weeks, and that the critical activities, in time order are C, H and I.