Start with the idea
Start with one number in one row, column, or 3x3 box. In this example, we are focusing on the number 9 in the row. Only one square in that row can still take 9, so that square must be 9.
Example
5
3
7
6
9
5
8
2
4
1
4
6
2
9
1
4
6
8
6
3
4
8
3
7
2
6
8
1
9
5
8
7
Look here firstLook across the highlighted row and focus on the number 9. Only one square in that row still lists 9.
This is a square-solving technique: the row tells you where 9 must go.
The target square can still show other notes. The important clue is that 9 has only one home in the row.
- Choose one row, column, or 3x3 box.
- Focus on one missing number.
- If only one square can hold it, place it there.
square to fillother cells in the row
When to look for it
Use it when a row, column, or box still has several empty cells, but one digit appears in only one note list.
How to use it
- Choose a row, column, or box.
- Scan one digit across all empty cells in that row, column, or box.
- If the digit appears in only one note list, place it there.
Common mistakes
- The target cell may still show several notes.
- The single is hidden inside the row, column, or box, so scan by digit, not only by cell.