You can add an almost unlimited number of WBS milestones, which can be used instead of activities to calculate earned value. WBS milestones are assigned at the WBS level, and each milestone is given a weight representing its importance in the project schedule. When you mark a WBS milestone as complete, P6 uses its weight to calculate the performance percent complete of all activities included in the WBS level. That is, the performance percent complete is applied to all activities under that WBS level and then aggregated to the WBS.
For example, suppose a particular level of the WBS includes ten activities, and actual finish dates have been entered for five of these activities. The same WBS is also assigned four WBS milestones having equal weights, but only one of these milestones is marked as complete. P6 uses the completed WBS milestone to calculate the WBS level’s performance percent complete as 25%, even though 50% of the activities included in the WBS level are finished.
In the initial stages of project planning, decide how you want P6 to calculate earned value, percent complete, resource use, and financial data. You might choose to use WBS milestones when higher-level task increments comprise a body of activities and you want to control the activities at the WBS level. For example, to control the design of a new product, you might assign WBS milestones to the major steps required to complete the design such as drafting the requirements, writing the design specifications, and so on. Each of these milestones would contain the detailed activities required to complete it.