Put your red and green glasses away, it’s not that kind of 3D. Three dimensional functions in Excel work across worksheets. Just like you can sum the range A1:A10 without identifying each cell as an argument, you can also sum all the A1’s in all of your sheets.
The syntax for a 3D Sum function is
In this example, the function sums A1 across the sheets Sheet1 – Sheet3. Multiple windows of the same workbook are used so that you can see the values on the different sheets.