Technique guide
Naked single
A naked single appears when an empty cell has exactly one legal candidate. The answer is visible in that cell's notes, so no comparison with other candidate positions is required.
When to use it
Use it throughout the solve, especially after placing another digit. Every placement changes the candidates in its row, column, and box and may create a new single immediately.
A small example
Suppose a cell in the lower-left box can initially hold 2, 6, or 8. Its row already contains 2 and its column already contains 6. Only 8 remains, so 8 is confirmed in that cell.
Step by step
- 1Choose an empty cell in a well-filled row, column, or box.
- 2List digits 1–9 that are absent from all three units.
- 3If one candidate remains, place it and rescan its peers.
Recommended level: Beginner; essential at every difficulty.
Put it into practice
Easy puzzles give you frequent opportunities to repeat this scan.