How do I prevent duplicate numbers from being entered in a column.
 

I am trying to set a check register example and want to prevent the user from
entering the same check number twice. Is this possible in Excel?

Select the column, assuming D1 is the active cell, for example, do this:
Use Data/Validation, select Custom from the first dropdown, enter this in
the Formula:
=Countif(D:D,D1)=1
then set the appropriate error alert in the error alert tab.

Bob Umlas
Excel MVP

"Clearwater Tim" <Clearwater wrote in message
...
I am trying to set a check register example and want to prevent the user
from
entering the same check number twice. Is this possible in Excel?