Sorry, does this help?
EDW
Item, Cal year / month, Historical Demand, Abs Error, Group
X, 03/01/2012, 100, 50, A
X, 04/01/2012, 100, 50, A
X, 05/01/2012, 100, 50, A
X, 06/01/2012, 100, 50, A
X, 07/01/2012, 100, 50, A
X, 08/01/2012, 100, 50, A
X, 09/01/2012, 100, 50, A
X, 10/01/2012...