Can anyone help.

I have some data being output to an excel worksheet and the number of rows
output is never the same.

I have written some code to find the last row used and then select the cell
in this row relating to a certain column. I am now having trouble insetring
a formula into this cell and copying this formula to all the cells above in
the same column.

a sample worksheet would look like this:

Tag num Jig Num Wgt A Wgt B Wgt Diff
1 100 90 95
2 101 85 95
6 130 110 150 *

The code I currenty have selects the cell * above, I then want to insert a
formula in there which subtracts Wgt A from Wgt B, then copy this formula
upwards in the cells in Wgt Diff Column to the row under the heading row.

Can anyone help?

Thanks