Thanks Bob for the macro. It has been interesting working through
what you have done with it as this is the first time I am working with
VBA.

Is it possible to get the macro to replace the existing values instead
of starting a new column?

Cheers - James

PS Richard thanks also for the simpler formula (I've just woken up -
West coast of Australia). I'm about to work through what you have done
with that as it does seem a lot simpler than what I was using.