Critical Path

August 19, 2009
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You have done your WBS. You have been able to sequence the activities for the most effective outcome of the project. You have organized so that structure of the project plan is clearly visible. What remains now is to represent the activities in a network diagram. This clearly shows you the interrelationships of activities. Each activity has a duration attached to them. This is the time it takes to complete the activity. No variability in the out outcome is taken into account, so use one number that you know to be fairly accurate. For each activity consider four other time parameters the earliest start, earliest finish, late start time and the latest end times. The difference in the late and early start as well as early finish and latest finish define the time margin or float. If the task were to start anywhere during the leading float and end anywhere within the trailing float the outcome will not be affected.

The Critical Path

When you traverse any path in this interconnected diagram if you add up the duration estimates as you go, it’ll tell you the total time it takes to go through the sequence of events that you traverse. The critical path is the path with the longest duration. The set of activities on this path have to be completed on time otherwise the total timeline of the project get extended. The Gantt Chart is a representation of such a network. The tasks/activities that represent the longest path is the critical path. Obviously then, any delay in completing any of the tasks on he critical path will delay the project completion. Also note that the overall duration cannot be reduced as there are no floats associated with the tasks on the critical path.

On the network diagram or the Gantt chart there will be one or more set of activities that cannot be optimized to reduce the time taken by reducing any floats associated with these activities. They do not have such floats. There will be many other activities for which start and stop times can have some margins. As long as the margins are not exceeded, the outcome is on time and does not affect the overall time schedule.

Watch the Critical Path like a Hawk

In general, you should be watching any path that have low or nil float. But, the critical path, the set of activities it represents, is the one to watch all the time. Monitor them more frequently if need be. Have resources available for these tasks al he time. You should not only be watching these activities, you should keep an eye on the other activities that have dependencies with any activity on your critical path. Essentially do whatever it takes to make carrying out of these tasks smooth.

To help monitor the project better and to make the critical path obvious. It is a good practice to lay out the critical path so that it is the central part of your chart. Other activities can be laid out that are parallel to these activities.

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