Formula to validate duplicates

[Gubbedelux]

Im trying to made a formula thats preventing duplicate entries in my worksheet. I want to check table A from position 8 to 3000 and give the user a varning message if a duplicate occurs.

Have tried videos from youtube but they did not work. A message allways pops up and till me to use an apostrophe in the beginning of the formula. PLEASE HELP

Bengt from Sweden

[#2]

@Gubbedelux 

use below formula for the data validation for desired range. Change all the "B"s to fit your need.

=COUNTIF($B$1:$B4;"="&B4)=1

[#3]

Thanks for you response. Another message poptup that says. ONE OF THE AREAS YOU MENTIONED COULD NOT BE FOUND. Do you have any other idea?.@erol sinan zorlu 

[#4]

@Gubbedelux 

Please check the attached file.

[#5]

Thanks it works like a charm. Thank you kindly

Best regards Bengt

@erol sinan zorlu 

[#6]

@Gubbedelux  lease mark this as best solution.