Hidden Pair

Two digits fit only the same two cells in a unit.

Learn the Hidden Pair Sudoku technique: two digits restricted to two cells let you strip every other candidate from those cells.

How to use it

1. Track two digits. In one unit, find two digits that can each go in only the same two cells.
2. Confirm the hidden pair. Those two digits must fill those two cells, even if the cells currently list extra candidates.
3. Clean the cells. Delete every other candidate from the two cells, leaving just the hidden pair.