Can I ask another.

I have some substantial Excel sheets with a lot of aircraft data on them. The person who put them together only put the aircraft serial number (one of the columns) against the first line for such, any additional lines (from none to say 20 of them) and the serial number column is just blank.

This is fine for just looking at the info, but if you want to sort the sheet on one of the other data columns to bring common things together, the serial number reference is then lost.

So, can anyone suggets a formula which says "if the cell is blank, then make it the value of the cell above, if that has something in it". Probably best to add an extra column to do this.