I have daily sales data for the last four years. I have created a pivot table
that shows sales by client and have grouped the daily sales information into
months and years. I only want to display the last thirteen months worth of
infomation. I can this to work quite easily.

I also want to show the percenatge difference in revenue between months for
each client. I can do this with no problem. The problem is that I can not get
the calculation to work to show the % difference between January 2009 and
December 2008. That calculation shows nothing. The calculation for the %
difference between December and November works fine.

I think that the problem may have something to do with how I have grouped
the data. Does anyone have any suggestions on how to correct this/