check for previous entry

[MichaelCasper]

I use column "D" for entering invoice numbers.How can I have Excel lock at
all previous enteries to see if I am duplicating an entry on any other row of
column "D"

 

[Max]

You could apply data validation on that col D

Select col D
Click Data > Validation
Allow: Custom
Formula: =COUNTIF(D,D1)<2
Click OK

Test it out ..
--
Max
Singapore
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