How do I keep from repeating a number in the same column?

[Stephanie]

In column A I have a series of numbers. How do I keep other users from
entering a number in Column A which is already present in Column A. So, for
example A2 has #3451. Another user enters #3451 in A10. I need a prompt to
let the user know #3451 has already been used.
Thanks in advance.

 

[Gord Dibben]

See Chip Pearson's site for using Data Validation to prevent duplicates.

http://www.cpearson.com/excel/NoDupEntry.aspx


Gord Dibben MS Excel MVP

 

[Jim Thomlinson]

You can try this... Place your cursor in Cell A2. Now highlight the entire
column. Now select
Data|Validation -> Custom
In the formula box add
=countif(A:A, A2) = 1

You will probably want to change the error alert message, but at this point
you should be good to go in terms of only allowing unique entries...

 

[Stephanie]

Hi Jim,

Thank you so much - it worked perfectly.