>Francis,
>
>You need to define a couple of report variables that contain the sum of X and Y. Call them SumX and SumY, their value is X and Y respectively and the calculation you're doing is SUM. The initial value is 0 and they are reset at the end of the group or report, depending on where your summary line is.
>
>The expressions for the total columns are therefore
>
>

SumX    SumY    SumX-SumY    round(((SumX-SumY)-SumX)/100,2)

>

I'm clearly missing something. Why is (X-Y)-X) not just -Y?