How to read the grids
- Given - clues from the starting puzzle
- Subject - cells the technique focuses on
- Eliminated - candidates this technique removes
- Candidate - pencil marks shown for reference
How to spot it
Look at empty cells where the row, column, and box together already contain eight different digits. The ninth is forced. Scan after every placement - placing a digit often creates a fresh naked single nearby.
5
6
8
9
9
1
7
2
4
8
3
6
5
7
8
Worked example
In the highlighted cell, the row already contains 1, 2, 3, 5; the column contains 6, 7, 8; and the box contains 9. Only 4 remains. Place 4.
Time to practice
Reading is half the work. Try a puzzle now and look for the techniques you just learned.