Pointing Pair

A digit confined to one box line eliminates it along that line.

Learn the Pointing Pair Sudoku technique: when a digit in a box is stuck on one row or column, clear it from the rest of that line.

How to use it

1. Find a box-locked digit. In a 3×3 box, find a digit whose only candidate cells all sit in the same row or the same column.
2. Point along the line. Since the digit must stay inside the box, it must lie on that shared row or column.
3. Eliminate outside the box. Remove the digit from the rest of that row or column outside the box.