I need help!

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

                 2008  2009  Total
Jan  BatchA     5        6        11
       BatchB     3        1          4

Feb  BatchA     1        2          3
        BatchB     0        1          1

In the total column instead of counting the row I want to subtract them.
I don't want 5+6=11
I want 5-6=-1

Is there a way to get this result?