computed field / field = computed field

I just started playing around with this module tonight so i may still be missing something so far every thing is working great when i am adding fields and making totals but what i would like to do is to take the output of a computed field and divide it by a number then add it back to the total.

best way to describe it would be like adding sales tax to a total and then making a new total but i am not dealing with money.