Pointing pair (locked candidates)
When a digit's only possible cells inside a 3×3 box all share a row or a column, that digit can be eliminated from the rest of that row or column outside the box.
A pointing pair (also called locked candidates, type 1) happens when a digit's only legal cells inside a 3×3 box all share the same row or the same column. Because the digit must end up in one of those box cells, and they all sit on a single line, the digit is locked to that line within the box. That means it can be eliminated from every other cell on the same line outside the box.
How to spot one
Pick a box and a digit that hasn't been placed in it. Look at the digit's pencil-marked cells inside the box. If they all sit on the same row, that digit can be ruled out from every other cell of that row in the other two horizontally-aligned boxes. Same for a column.
Worked example: in box 4, the digit 7 can only go in cells (4, 1) and (5, 1) — both in column 1. The 7 must end up somewhere in box 4, which means it must end up in column 1. So every other cell of column 1 outside box 4 — cells (1, 1), (2, 1), (3, 1), (7, 1), (8, 1), (9, 1) — can have 7 ruled out as a candidate.
Why "pointing"
The pattern points the digit's claim outward from the box into the rest of the line. The box owns the digit; the line carries the elimination. The shadow technique — same logic, opposite direction — is box-line reduction, where a digit confined to a single box within a row or column eliminates that digit from the box's other cells.
When you'll see it
Pointing pairs (or pointing triples — the same logic with three cells) are common from medium puzzles upward and are usually the move that follows the naked-and-hidden-singles cascade. Without them, most medium and hard puzzles would stall. They're often the gateway move that opens a fresh round of singles in adjacent units.
For a longer walk-through alongside its sibling, see Pointing pairs and the snake.
See also
- Box-line reduction (locked candidates)— When a digit's only possible cells inside a row or column all sit in the same 3×3 box, that digit can be eliminated from the rest of that box.
- Hidden single— A digit with only one possible cell within a unit (row, column, or 3×3 box) — even if that cell could legally hold other digits. The unit-first sibling of the naked single.
- Candidate— A digit (1–9) a cell could still legally hold — one not yet ruled out by anything in its row, column, or 3×3 box. Every empty cell has between one and nine.
Read more
- Pointing pairs and the snake
The pointing-pair pattern is one of the most useful mid-level moves in Sudoku — and one of the easiest to miss. Here's the perceptual habit that surfaces them.