Naked Pair
Two cells in a unit share the same two candidates.
Learn the Naked Pair Sudoku technique: two cells limited to the same two digits let you eliminate those digits from peers.
How to use it
- Spot two matching cells. Find two cells in the same unit that each have exactly the same pair of candidates, e.g. {3,7}.
- Lock the pair. Those two digits must occupy those two cells (in some order), so no other cell in the unit can use them.
- Eliminate from peers. Remove both digits from every other cell in the shared unit, often unlocking new singles.