Pivot table problem

[buffalo]

Hi,

I have three entries in the data columns, say
Data1 Data2 Data2
The rows are for dates and columns for accounts

Now I need to add a new column (in the pivot table) so that Entry(i) =
Data1(i-1) + Data(i-1) - Data3(i-1).

Ofcourse I could just do Value(i-1) = Data1(i-1) + Data(i-1) - Data3(i-1)
(i.e make another data entity as Data1+Data2-Data3)
and keep it in my mind that Value(i-1) will actually correspond to the next date... But i wanted this to be cleaner... and the entry in this new entity correpond properly to the date.

thanks again.