This seems like it should be so easy, but I'm having trouble with it.

Here's my example:

I have a pivot table with 2 fields. One is budget and the other is actual.
I want to add a field that shows me the difference between the 2 columns. I
am trying to do this by adding the actual column to the data field again and
then changing its appearnce with the "Options" button. I've selected
"Difference from" under the heading of "Show Data As." I've then selected
the budget as my Base Field. What should I be selecting for Base Item? It
seems like this should be intuitive. Anyway, regardless of which base item I
select, I get a blank column.

I can certainly calculate my difference off to the side of the pivot table,
but it seems like there must be a better way.

Thanks for your help!