Pointing (Locked Candidates)
A Sudoku solving technique · level 2 · first needed around SE grade 3
By The Hardest Sudoku Team · Last updated
TL;DR
Pointing is when all candidates for a digit inside a box fall on a single row or column, letting you eliminate that digit from the rest of that row or column.
How does the Pointing (Locked Candidates) work?
If, within one box, a digit's only possible cells all share a row (or column), then the digit must end up in that box on that line — so it cannot appear elsewhere along the line outside the box.
When does it apply?
When a box confines a digit to one of its lines, you 'point' the elimination outward along that line.
A worked example
If 4 in the top-left box can only sit in the box's top row, then 4 is removed as a candidate from the rest of that top row in the other two boxes.
See where this fits on the difficulty scale on the SE grade page, or browse every technique in the glossary.