I have a table of data

Month Hours
Jan 06 2005
Feb 06 1750
Mar 06 3520
.....
Mar 07 2300


I have a table on a separate sheet. I want to be able to put (say) Mar 07 in
cell A1, and have the 12 month moving total (total from Mar 07 to April 06)
in cell A2. If I change A1 to Feb 07, then the 12MMT range is from Feb 07 to
Mar 06, and I want the total to change to reflect this.

Can someone help with a formula please

Thanks,

Rob L