This is brilliant - excatly what I am looking for. However there is one more item that needs to be figured out. I have another forumla which is giving the values in both columns A & B, so some of them are 'empty' and showing #N/A. So those formulae seem to be given a value of zero in a set of data with #N/A is present. Is there a way to tell the formulae to ignore #N/A entries?