How can I format cells so that if I add say 10 degrees to a compass value of
355, Excel will return 005 rather than 345; in other words I want to work in
base 360.

I assume you meant "005 rather than 365", and not "005 rather than 345"?

Try =MOD(A1+B1,360)
--
David Biddulph

"Stephen" <(E-Mail Removed)> wrote in message
news:2569D08B-BD79-43D7-A7A0-(E-Mail Removed)...
> How can I format cells so that if I add say 10 degrees to a compass value
> of
> 355, Excel will return 005 rather than 345; in other words I want to work
> in
> base 360.