Duplicate names in columns

[Quagga]

My spreadsheet contains part names and part numbers in columns.
I want to be flagged and not be able to enter a duplicate name in the same column.
I know this sounds simple, but I just can't find the solution.

[contaminated]

Would you like to read or watch ????)))

[sweep]

Hi,

Highight column A

Go to Data > Validation > Custom

Enter this formula

=COUNTIF($A:$A,A1)=1

repeat for as many columns as required

[Quagga]

Hi Sweep
Thanks for the help.
The solution you gave me, helps when I type in the values in that column.
I still have a problem when I copy and paste(Values) from another sheet, the duplication is not picked up. What do I do to resolve this one?

Thanks
Quagga

I have solved the problem by using conditional formating to highlight the names that were copied and duplicated.

Thank you Contaminated and Sweep for your help.