Scanning / Cross-Hatching

What It Is

Scanning (cross-hatching) is the basic strategy: systematically look at each number 1–9 and “cross-hatch” through rows, columns, and boxes to find lone positions. Use numbers already placed to block where new numbers can’t go until one spot remains.

When to Use

Use cross-hatching right at the start and whenever you’re stuck early. It shines when a number is missing in almost every box and often yields quick footholds.

How to Apply (Step-by-Step)

Pick a number: start with 1 (or any digit) and scan all rows, columns, and boxes for that number; mark the 3×3 box missing it.
Cross-hatch lines: in that box, draw lines through any row/column that already contains that number elsewhere; those lines show where it cannot go.
Find the single open cell: after eliminating with cross-hatching, if only one cell remains, place the digit there.
Repeat for all numbers 1–9: go box by box or number by number; you’ll often place several easy numbers.
Scan each row/column too: reverse the process by picking a row/column to see if a number can only go in one position there.

By scanning systematically, you’ll catch many hidden singles. For example, if every cell but one is eliminated for digit 7 in a box, that last cell is a 7. After each placement, new opportunities appear—keep cross-hatching until no single-choice moves remain.

Be patient and thorough. After every placement, re-scan; cross-hatching often chains into fresh singles.

Scanning / Cross-Hatching

Scanning / Cross-Hatching

What It Is

When to Use

How to Apply (Step-by-Step)

See also