Naked pair in Sudoku

How it works

Say two cells in a row can each be only 1 or 3. If one is 1 the other is 3, and the other way round. You cannot tell yet which is which, but you do know that both digits will be used by these two cells. No other cell of the row can be 1 or 3, so you can erase those notes.

If the two cells also share a box, the pair clears the rest of that box as well as the line.

1. Fill in pencil marks for a unit.
2. Look for two cells whose notes are the same two digits and nothing else.
3. Remove both digits from every other cell of the unit.
4. If the pair shares a second unit, clear that one too.

A real example

The two blue cells hold the same two candidates. Any red candidate in the same unit is one of those digits and is removed.

How to spot them

A naked pair is the easiest pattern to see once notes are on the board: look for cells with exactly two notes, then check whether another cell in the same row, column or box has the same two. In Sudoku Clan, turn on Notes and fill in the candidates, and matching cells are easy to compare.

Common mistakes

• Treating cells with three notes as a pair. Both cells must have exactly the same two candidates. If two digits are confined to two cells that also have other notes, that is a hidden pair, and it works differently.
• Pairing cells that do not share a unit. Two matching cells in different rows, columns and boxes tell you nothing.
• Working from incomplete notes. A missed candidate makes a false pair.