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Pointing Pairs Explained

What it is

A pointing pair is born inside a 3×3 box. If a candidate can only sit in two (or three) cells there, and those cells all fall on the same row or column, the candidate is pinned: wherever it ends up inside the box, it will occupy that line. Which means that along the rest of that row or column — outside the box — the candidate cannot exist, and it can be erased.

The box "points" at the line: hence the name. It's an interaction technique: rather than examining one unit in isolation, it exploits how a box and a line constrain each other. Its mirror image, box-line reduction, reasons in the opposite direction: if, within a row, a candidate survives only inside one box, it's erased from the rest of that box. Same principle, reversed — and they're worth hunting for together.

A practical note: pointing doesn't demand complete pencil marks across the grid. You only have to answer, for one candidate and one box, the question "where can it still go?". That's why it's often the first elimination players learn to see with the naked eye.

How to spot it, step by step

  1. Pick a box and a candidate not yet placed inside it.
  2. Note which cells of the box can still take that candidate.
  3. If the possible cells number two or three and lie all on the same row or column, you have a pointing pair (or triple).
  4. Follow that line out of the box and erase the candidate from every pencil mark you meet.
  5. Repeat with the same candidate in the other boxes: pointing patterns tend to come in runs.

The example in the diagram

5 2 7 5 9 1 2 6 3 4 8 2 6 9 6 3 5 8 1 9 5 7 4 Inside the box, 5 can only sit on the top row: outside the box, along that row, every 5 is erased.

In the box on the left, candidate 5 survives in just two cells — both on the top row (highlighted). The box's 5 will land in one of those two, which means the cells of that same row outside the box can't hold it. The two 5s pencilled further right are erased.

Common mistakes

First: eliminating the candidate inside the box instead of outside. The pointing cells are the constraint, not the target. Second: trusting stale pencil marks — if a third possible 5 existed in the box and you never noted it, the pointing pair doesn't exist and the elimination is an error. The technique is only as good as your candidates.

Where you'll need it

It's one of the techniques that define medium sudoku, alongside Naked Pairs — and here, tiers and puzzles are graded by exactly these. The other guides live in the techniques index.