On the last page, I'd like to be able to show the average of the cost difference by Project ID, which is Group Header #1 and Group Footer #1. The formula field "Display Difference" is not available to select for a running total formula. Also, if I try to select that formula field and use Insert Summary, the field is not available to summarize.
I'd like to show the average of the Display Difference numbers in the project id / Group Footer #1 area. See below.