Adding the Sum of Total till the Month Shown in the Cross Tab Report in Crystal Repor

I have developed a cross tab report in crystal report 2008. which shows the item wise sales data for every particular month grouped by the Division.

Which looks like this v2jj8.jpg at Free Image Hosting

But now i want the Sum of The Total for that Particular month + Sum of Total for all previuos months.

For example : May-06 = Sum 0f May-06 + Apr-06 + Mar-o6 + Feb-06 + jan-06 + Dec-05 + Nov-05 and so on till the data exists. May-06 = 16012.50 + 21088.00 + 0 + 0 + 0 + .....

Please send the procedure or code in detail.

Regards, Mohammed Irshad.