Copying formulas from a row down to a row across
 

How do I copy values from a row down Sheets 1 and 2:
A B
1: 1/2/2009 0
2: 1/9/2009 0

Into a formula in a row across in Sheet 3?:

A B

1: 1/2/2009 1/9/2009

2: ='Sheet1'!B1+'Sheet2'B1 ='Sheet1'!B2+'Sheet2'B2


I'm trying to do this without having to go into every formula and manually
type in the correct cell numbers for the reference. (I have to show this
calculation for at least 15 different criteria for every week and month end
of the year, so quick math says manually editing nearly a 1000 cells would be
a pain.)

Copying formulas from a row down to a row across
 

Excel 2007
Pivot Table
No formulas needed, automatic week/month grouping:
http://www.mediafire.com/file/yj2wg15knty/12_24_08.xlsx