Googlesheet-duplicat-cell



First, select the names in the dataset (excluding the headers).
Click Format > Conditional Formatting 
Click Add another rule on the Conditional format rules side panel.
Under Format rules, click Format cells if… and select Custom formula is from the drop down menu.


=COUNTIF($C$1:$C$1000,C1)>1

C = kolom 
C0 = start
C18 = end