How about using a helper column. If your serial#'s are in columnA in cell
B1 enter

=IF(OR(A1="",COUNTIF(A:A,A1)<2),"","Dupe")

and copy it down. It will show nothing if there is no entry in the
corresponding cell in A or if it is not a dupe. If there is a dupe it will
show Dupe in BOTH/ALL duplicated cells

--
HTH
Nick Hodge
Microsoft MVP - Excel
Southampton, England

HIS
www.nickhodge.co.uk

"Dgwood90" wrote in message
...
I want to create a spreadsheet that when a number is entered, it will state
whether that number is already in the spreadsheet or if it is not located.