During our Primavera P6 training classes (www.primaverascheduling.com) we always stress that activity durations must be “measurable”. By this we mean that activity durations must be of a reasonable length so that problems can be spotted right away. Assume that you were trying to update a task that is expected to take six months. How would you measure progress after one month? You might be tempted to simply reduce the remaining duration by one month – i.e. you assume that everything is proceeding according to plan. Obviously this is a risky approach. We update schedules to validate that the plan. Otherwise, why bother updating at all?
Experienced P6 schedulers know that activity steps are a way to measure progress on complex tasks, but this approach is not a substitute for proper durations. Activity steps have no logic or durations and therefore do not provide any feedback as to what exactly is taking too long. Moreover, activity steps also require using the physical percent complete setting for updating tasks but this is not always practical or desirable.
So what exactly is a measurable duration? A good rule of thumb is that activity durations should not be any longer than the update period. If the schedule is updated once a month then the activity durations should be a month or less. When an activity starts during one update period it should finish during the next update period, or be very close to finishing. Activities cannot hide their lack of progress when durations are limited to the length of the update period. Procurement activities sometimes need longer durations as a matter of necessity but certainly for field activities there is no reason not to keep durations reasonable.
As professional schedulers we have been following this approach for 30 years with great success.