Hi Pete, Thanks for your help.

I should have clarified. The bulk of the N/A's can be ignored as they won't match the location ID. My problem is there is 2,570 station IDs (Column A) and the same amount of values in Column B. For whatever reason, both your formulas and mine, only return a match for 2,466 values, instead of the 2,570. I've found a few instances where 3 of 4 duplicates will have the correct value returned, but the fourth one is ignored entirely. Does this help?