From Excel HELP:
note: you will need the "SUM" function....
Refer to the same cell or range on multiple sheets
A reference that refers to the same cell or range on multiple sheets is
called a 3-D reference (3-D reference: A reference to a range that spans two
or more worksheets in a workbook.).
Click the cell where you want to enter the function.
Type = (equal sign), enter the name of the function, and then type an
opening parenthesis. e.g. "=SUM(" [no quotes]
Click the tab for the first worksheet to be referenced.
Hold down SHIFT and click the tab for the last worksheet to be referenced.
Select the cell or range of cells to be referenced.
Complete the formula, and press ENTER.
When done your formula will look something like this:
=SUM(Sheet1:Sheet3!B23) [you will need to adjust the sheet range to fit your
needs]
HTH
Bruce