Cross-Hatching (Column)
When a number has only one possible cell left in a column.
Explanation
Pick a column and a number. Rows and boxes that already contain the number block cells in the column. If only one cell survives, the number goes there.
Practice tip
Check each empty cell of the column against its row and box.
Example steps
- Pick one column and one number to track.
- Cross out column cells whose row or box already contains the number (mark ✕).
- Only one cell in the column survives — that is where the number goes.