need to show a blank form field if the amount is

Hi all. I have a form set up that calculates across rows, and totals those rows. Then it takes the total and subtracts it from an advance. I have it showing on two different lines (depending on if it is an overpayment or balance owing) if it is the negative, I'd like that field to show nothing.

So instead of showing:

Overpayment    -$341.00

Balance              $341.00

I want it to show

Overpayment

Balance             $341.00

and vise versa

I've tried using the validation section but it doesn't seem to work for me. it always shows an amount on both lines.