Try this out. I know it's a little lengthy, but it's not as bad as it looks:
Say you have 3 sheets of data. The first sheet is the Grand Totals (GT). The other 2 sheets have the rest of the data (subtotals) you want to add together, the result being on the GT sheet.You want the names of the products end up in GT's column A; the total cost of them in B. DataSheet1 has the product names in A and the costs in B. DataSheet2 has names in B and costs in C (note the values are in a different place than the first datasheet...)
Here's how you do it:
In GT's cell A1 type an equals (=) then click on the first datasheet tab then cell A1 (the first product name). [Enter]
Now in GT's cell B1 type: =sum(datasheet1!A1,datasheet2!C1) [Enter]
You can drag these formulas down as far as you need.
Woops. the formula at the end for cell B1 should be: =sum(datasheet1!B1,datasheet2!C1)
Change "A1" with B1