PivotTable Calculated Field

You want the average as in if N- is one and D- is zero, you want 0.5 per line and you do not want the sum of the averages, but the average of the sums. OK confusing so an example

N | D
1 | 1
1 | 0
0 | 0

The average per row is 1, 0.5 and zero respectively.

The total is 2 Ns and 1 P which is 3 and there are three rows, so the average is 1. If this is the logic you want, you will have to add a helper column to the source data. Call it NumRows and fill it with =1.

Then the average is (N + P) / Sum of NumRows.

I think that would get you the answer you want.

BTW: Since you have Office 365, you should consider having the data in an Excel Table. This way if you add rows or columns all you have to do is refresh the pivot table. Tables always reference the right amount of rows, and if you added a new column, it will not be available to the pivot table.