How to solve a naked pair in Sudoku
A naked pair is two cells in a unit that hold the same two candidates, which lets you remove those digits from the rest of the unit.
How it works
If two cells in a row, column or box both have only the candidates 3 and 7, those two cells will use up the 3 and the 7 between them, in one order or the other.
So 3 and 7 can be removed from every other cell in that unit. The digits are not solved yet, but the rest of the unit gets simpler.
How to spot it
Look for two cells in the same unit with exactly the same two notes. They do not have to sit next to each other.
A worked example
This is a step from a real puzzle, a moment where the next move needs a naked pair.
Struck-through digits are the ones that can be removed.
R4C2, R8C2 can only hold 4, 8 (a naked pair), so those digits can't go anywhere else in column 2. Remove them from R5C2, R9C2.
Where it fits in Rocksled Sudoku
Puzzles that need a naked pair are never rated below Hard. Each step of this kind adds 16 points to a puzzle’s difficulty score. When you ask for a hint that needs it, the game names the technique and shows the cells involved. See how to play for the rest of the controls.