I'm making a matrix like so....

Code:
 
            
                                1/2008           12/2008           Difference
Yellow
            Active                 4                    10                 +4
            Not Active           15                   8                  -7
Blue
           Active                  8                    14                 +6
           Not Active            20                  18                 -2



So I've got a count of objects grouped by its color and status... and also grouped on the date the object and its status were created.
Problem is... I can't seem to figure out how to add that difference column to the matrix. I want to make it look much like a total column if I were to have one. In fact if I could just add a total column and then change the expression that would work. But I can't find how/if you can do that in Reporting Services 2005. Anybody have the answers? I'm googled out right now