Cross-Hatching
Disciplined scanning aimed at one box: use the rows and columns crossing it to eliminate cells until a digit has exactly one home.
A 3 in this row and this row already block six cells of the box.
How to spot it
- 1Focus on a single box and a single digit.
- 2Draw lines from that digit's occurrences in the intersecting rows and columns.
- 3Whatever cell survives the crossfire is the placement.
When to use
When a box is nearly full — cross-hatching finishes it fast and cleanly.
Common mistake
Jumping between boxes mid-scan. Finish one box before moving on to keep your search organised.
Worked Example
Cross-hatching is scanning made deliberate: instead of sweeping the whole board loosely, pick one box and one digit, and work only the three rows and three columns that pass through it. Suppose you're hunting for where 3 goes in the center box. Two of its rows already carry a 3 elsewhere on the board, blocking six of the box's nine cells outright.
Two of its columns carry a 3 too, and their lines block two more of the remaining cells. That leaves exactly one cell the 3 can still occupy — place it. Working one box at a time like this, rather than jumping between boxes mid-scan, keeps your search organized and makes sure you don't skip a placement.