Macros are VERY slow to run

[wxtoad]

I think it's because when each function is executed, it goes all the way down to bottom of the spreadsheet, well beyond the last row data. When I look at the sheet after executing a function, it has placed a "0" in all cells in the column below the data. Then when the next function executes, it goes all the way down to the bottom and attempts to do something with the "0"s.



My sheet contains only 27,000 rows. Is there some way to limit calculations to only those rows and no further into the blank portion of the sheet?
I record the macros - so far VBA is beyond my skill set.

Thanks,
WxToad