I need help!

I got a crosstab, and I'm trying to show the difference between rows. I got something like this:

                 BatchA  BatchB Total
Jan 2008       5          1          6
      2009       2          2          4
     TOTAL      7          3         10

Feb 2008       0          1          1
       2009      1          1          2
       TOTAL    1          2          3

In the total ROW counting the row I want to subtract them.
I don't want 5+7=7
I want 5-2=3

Is there a way to get this result?