Formula for Rolling Average from Multiple Worksheets

[rstotty]

Hello,

I'm new to this forum. I am trying to create a moving average formula that pulls data from 2 worksheets. Worksheets are arranged using columns B1:M1 to represent January - December. Data (in %'s) begins in cells B2:M2 and each worksheet represents a year (ie. 2011,2012). I need worksheet "2012", cell "O2" to calculate a rolling average using the data pulled from worksheet "2011, cells N2,M2 (November, December) and worksheet "2012, cell B2 (January). This needs to update the 3 month rolling average as I add each month. I have the correct formula as long as the data is pulled from the same worksheet but my problem is when the data spans 2 worksheets. Any help would be greatly appreciated. I've attached (hopefully) an example of my spreadsheet.