To make sure I understand the pattern of the calculation, does the window subtract two months each subsequent year? I.e. would the April 2012 total=avg(Apr2012 - Mar2012)?
pattern is avg 6 months diagonally,
Column June 2012 Tot = Avg(4.49%,6.53%,4.2%,5.8%,5.47%,5.53%)
May Tot = Avg (41.08%,38.61%,40.43%,42.68%,42.93%,43.00%) and so on.
it's easy in excel.....
Many thanks to James Austin from Interworks for solving this for me.
For the benefit of the forum, it would be great if you could post the solution you've found for anyone looking at a similar problem.