To ignore the first occurrence and highlight only subsequent values, use this formula:
If you want to check for duplicate values across multiple columns, concatenate the values and apply a similar rule to the results, as shown in the figure above. You can also hide duplicates (which I don't always recommend) by selecting a font color that matches the sheet's background.
Susan Sales Harkins is an IT consultant, specializing in desktop solutions. Previously, she was editor in chief for The Cobb Group, the world's largest publisher of technical journals.