Can you mock up what you are looking for as an end-result? I'm not sure what "month on month increase in performance" is referring to. Posting a packaged workbook is a great start, but I'm not sure I understand what you want as an end result.
If you could create an end result mock up that would be great.
But if you're just trying to do a month over month comparison you can use table calculations to create a running total, difference from previous month, or % difference from previous month like in this pictures. You just click on the little down triangle to the right of the measures pill box and choose the table calculation you would like. I'm not sure if that helps at all.
What I actuallly want to be able to do is to look at the impact th amount of training that a person has in, say month 1 and the impct that training has on their performance for the following 1, 2, 3 or 4 months - not sure yet how long that future period needs to be.
I also want to be able to compare at a aggregated level - to compare the effectiveness an impact of training delivery between teams.
Intuitively I think this involves a combination of calculated dimensions and table calculations but i can't quite work out how - particularly when it looks like i need to number of periods I look into the future to be ableto be easily varied.