I have created a worksheet that lists identification numbers for valves and
instruments on filtration machines. Now these identification numbers are
unique because they are a combination of both letters, number and characters.
I need to find a way to check if any of these indentifaciton numbers have
been duplicated in a column. No 2 numbers are the same and again I need to
know how I could check a column in excel for possible duplicates to correct
them.

Thanks