Greetings all,

oh hear me, practitioners of spreadsheetery, and heed my humble plea
for aid... I'm struggling with finding duplicates based on the values
in two columns. Basically, I've got people entering a list of IDs in
one column and a list of values in another. I want to make sure they
don't accidentally enter the same value for any given ID more than
once. Example:

ID Value
123 June
123 July
123 Feb
123 July <- duplicate
295 March
477 September
477 December


The desired outcome is to either prevent them from entering a dupe via
data validation, to use conditional formatting to flag dupes.

thanks!

..o.