Warning for duplicate entry in Excel - Serial Number Tracking

[RMEdgeGuard]

I am trying to setup a spread sheet to track random serial numbers. Is there
a way Excel will warn me if I make a mistake and enter a duplicate number?

 

[Beth Melton]

You can use Data Validation for this. Here's an article that contains
additional details:
http://www.cpearson.com/excel/NoDupEntry.htm

For example if you want to protect column A then the formula would be:
=COUNTIF($A:$A,A1)=1

Also note the links at the bottom for other alternatives such as
finding duplicate entries in a worksheet you have already created.

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Beth Melton
Microsoft Office MVP

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I am trying to setup a spread sheet to track random serial numbers. Is there
a way Excel will warn me if I make a mistake and enter a duplicate

number?