One way via Data Validation ..

Select col A

Click Data Validation
Make the settings:
Choose under "Allow:" : Custom
Formula: =COUNTIF($A$1:A1,A1)<=1
Click OK
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Rgds
Max
xl 97
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GMT+8, 1° 22' N 103° 45' E
xdemechanik <atyahoo<dotcom
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"bdq17" wrote in message
...
How do I get excel to automatically detect and notify when I've typed the
same number in two cells of the same column? I get a lot of duplicate
product
numbers that I imput into column A of my spreadsheet. Example: If I type
the
number 123456 into A1 I don't want that number in any other cell of column
A
and I want excel to notify me if I type a duplicate.