We have a pivot table of this form:

Type SubType Amount
a a 3
b 7
a Total 10
b a 11
b b 15
b total 26

We need to get another column to percent the amount as a percentage of the
subtotal rows...

for instance, 3 is 30% of the 'a Total' subtotal, 7 is 70%, 11 is 42.3% of
26, 15 is 57.7% of 26

etc.

I can't seem to find the right setting to do that.
Help?