How do I prevent entering duplicate numbers in an excel worksheet

B

Bran5956

I have a lot of bill laden numbers I need to keep track of in an excel
worksheet for accounts payable and I want to prevent entering duplicate
numbers. Is there a way I can have excel tell me when I have keyed a
duplicate number?

Thanks for any help.
 
J

Jim Thomlinson

You can use validation to do this... Select Data -> Validation -> Custom and
insert the following formula (Select all of column A with Cell A1 as the
active cell)

=COUNTIF(A:A, A1)=1
 
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