Subtract sub columns in Pivot table

[marketpupil]

I am trying to compare old system data to new system data so I made a pivot table. I am trying to subtract each 2 column subset, meaning I have the row as each department number, then I have 26 periods as columns. Each of those periods has two columns "new" "old", this is what I want to subtract. I do not know how to make a calculation field for what I will call the sub columns?

if anyone knows how to add a screen print to the thread let me know and I can add!

Here is a failed attempt of what PT looks like without gridlines

____________Column Labels
____________Sum of period 1_________________________________Sum of period 2 and so on............
Dept Numb____New KH_______Old KH__________________________New KH_____Old KH
50052615_____4,394.18______4,394.18___I want difference here____4,654.62_____4,654.62___DIFFERENCE HERE and so on....

 

[pbornemeier]

Please use Excel Jeanie (see link in my sig) to post a portion of your actual source worksheet and a part of a mockup of your desired PT.