Is this possible (Pivot table)

[Mr930]

I have a pivot reading a set of data that has 3 fields: DATE, SYSTEM and CATEGORY. There are 15 possible systems and 3 possible CATEGORYS and 240 DATES.

My table has SYSTEM and CATEGORY as my column headings and DATE as my rows.

I want to be able to calculate for each CATEGORY what its percentage it is of the total of all CATEGORYs for each SYSTEM. I can see how to do it as a percentage of the grand total for the row, but not subgrouped by SYSTEM.

Is this possible? Hope my description makes sense.

thanks
Fred Emmerich