Hi Ron,
This might appear twice, something seemed to go wrong first time.
Anyhow, thanks Ron, I just tried A2-A1 and it worked so I assumed all
calculations would be fine. Looks like a classic case of "When one
assumes one puts an ass before u and me".
I'll try to be more careful in future, but with so much to learn about
Excel I can't make any promises.
Ken Johnson