Chip - I've been trying SUMIF, but can't seem to get it to work. Have
also used DSUM without success. It may be that I just haven't got my
head around them.

Trouble is, I'm inheriting a spreadsheet that was 'designed' by someone
else and has become well established and liked by the users so I can't
change the structure too much.

But thanks for the suggestions so far, Guys. I won't be able to try out
these things for a day or so but will report back when I do.

Cheers

Will