You guys really know your stuff. I once spent 2 weeks doing a single advanced spreadsheet (that taught me most of what I know - but you guys come up with some great formulas!)
It assigns a value of 1 to the first of the series of duplicates, BUT it also assigns a value of 1 to the unique values. (i.e where col a has only 1 reference in col b) - for unique values it must assign a 0. I changed the first =1 to >1 and it worked like a charm! :-)
Just a very big thank you for all your help. I'm sure I'll come across a few more queries as I complete my spreadsheet.
Should I leave this thread open in case I come across any more queries for my spreadsheet or should I open up a new thread for them?