Trying to find a way in the pivot table expression to subtract a month from the previous month before it for all fiscal periods. We are currently pulling in each month as a YTD number so subtracting the previous months YTD # gives us the true monthly number. For instance- Period 4 is the sum of period 1-4 minus the sum of period 1-3. I feel like there should be a simple way to do this within the expression but I cannot figure it out for every single month.
I am still very new to this software so all help is appreciated.