Hi: Re: fig 7-8, P213, PMBOK 5.

I thought I understood how the project costs roll up from activites, to WBS, contingency reserves to come up with the Cost Baseline.

My expectation is that the sum of the activity costs is equal to the sum of the WBS components as my understanding is that the activity costs are just a further decomposition of the WBS.

However per Fig 7-8 P213 in PMBOK 5 this is not the case.

It indicates the sum of activity costs to be less than the sum of the cost of WBS component costs. The diagram illustrates a new "Activity Contingency Reserve" distinct from "Contingency Reserves" also illustrated. It is using the "Activity Contingency Reserve" to make up the difference. The contingency reserves are still there so it's not just another name for contingency reserves.

If you look at the diagram it will be immediately obvious to you what is going on - just can't explain it!

Apologies I can't post the diagram.

Any explanation re this situation would be appreciated.

Brian.