Excel 2003

I have 99 tabbed worksheets in one workbook. All 99 have the same template.
Each template collects a weeks worth of data and calculates a year to date
column. I have grouped sheets 2-99 and on the active sheet 2 entered the
following formula.

=+Sheet1!E13+Sheet2!D13

Sheet1 E13 being the previous week year to date. Sheet2 D13 being this weeks
total.

Problem: The formula in all sheets 3-99 always look at the data in Sheet1
and Sheet2 as if the formula read =+$Sheet1$E13+$Sheet2$D13. How do you make
it quit.