How to solve a naked single in Sudoku
A naked single is a cell where only one digit can still go, because the other eight already appear in its row, column or box.
How it works
Every cell sees 20 others: the rest of its row, its column and its box. Any digit already placed among those 20 is ruled out for the cell.
When eight of the nine digits are ruled out, the ninth is the answer. It is the simplest move in Sudoku, and most of an easy puzzle is solved this way.
How to spot it
Look at cells in crowded rows, columns and boxes first. A cell with eight neighbors in its row and box is usually close to a naked single. With pencil notes, it is simply a cell with one note left.
A worked example
This is a step from a real puzzle, a moment where the next move needs a naked single.
Struck-through digits are the ones that can be removed.
R4C5 must be 6: the other eight digits already appear in its row, column or box.
Where it fits in Rocksled Sudoku
Puzzles that need a naked single are never rated below Easy. Each step of this kind adds 1 point 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.