I have a worksheet with 2 columns of numbers (column A and column B) and I want to populate a 3rd column (column C) with values that only appear ONCE in both columns. That means any value that appears in column A and does NOT appear in column B, and vice versa. I've been looking for a solution all day and can't seem to find one. I want to stress that I'm not interested in a list of unique values (sans duplicates), so Advanced Data does not help me. Column C must not contain any values found in both columns.