"bdq17" wrote...
How do I get excel to automatically detect and notify when I've typed
the same number in two cells of the same column? I get a lot of duplicate
product numbers that I imput into column A of my spreadsheet. Example: If
I type the number 123456 into A1 I don't want that number in any other
cell of column A and I want excel to notify me if I type a duplicate.

Are you generating these product numbers yourself? If so, you're misusing
your computer. If you want distinct product numbers, just add 1 to the
previous product number - done.