When you see the #VALUE error, it means that there is something wrong with the way the formula is typed, or there is something wrong with the cells you are referencing.

If Excel is not highlighting cells in the formula, enable 'Allow editing directly in cells' and 'Enable fill handle and cell drag-and-drop' in Excel options.

How to highlight values Excel has a built-in conditional rule that highlights unique values. You don’t have to come up with a special formula—you just run though a few clicks.