Copy an equation down to the last row.

Hello,

I run a macro to import data from another file. Everytime the data is imported, the number of data rows changes. The data goes from column A to column Y. In column Z I have an equation. This equation should be copied down for all the rows. Meaning if the last row is row 208, the equation should be copied down to row 208. Then next time before the data is imported, the column should be cleared (except for the first row--so that I have the equation in a cell) and then copied down to the last row again, which might be row 104 or 350...etc. (Meaning if the data rows decrease, the equation should not go past the data rows).

How can I do this?

Thank you in advance for your help!

Sincerely,

az!