Subtracting Averages in a Pivot Table

[windsorben]

I have Spring and Fall scores being displayed as averages in my pivot table. I'd like to add a calculated field (to my pivottable) that subtracts the spring and fall averages. However, it will only subtract the SUM of the spring and fall scores. Does anyone know how to subtract values (displayed as averages) in a pivot table. I can manually write the formula to the right of the pivot table but I want it to be part of the pivot table (so it updates automatically).
Thanks!

 

[mole999]

Thought, if you remove the averages, do you not change the overall values that the averages came from, thereby changing the average !!