Sudoku technique
Pointing pairs
A digit trapped inside one box, and inside one line within that box. It has not been placed — but it has already been ruled out of the whole rest of that line.
What a pointing pair is
A pointing pair is a digit whose only remaining homes inside a 3×3 box all sit in the same row or the same column. Because the box has to contain that digit somewhere, and every candidate cell lies on that one line, the digit is guaranteed to land on that line — so it can be removed from the rest of the line outside the box.
Three cells works exactly the same way and is called a pointing triple. The name comes from the picture: the candidates in the box point along a line, and everything they point at loses the digit.
Why it is the best-value technique on a hard board
Because it needs no pattern-matching across the grid. Everything happens inside one box, you can check a box in a couple of seconds, and there are only nine of them. Compare that with an X-Wing, which requires comparing every pair of rows for every digit.
In practice, pointing pairs unlock a large share of hard puzzles on their own, and they are the technique most often missing when someone says a board is stuck. If singles and pairs have run out, this is what to try next — before anything more exotic.
Step 1 of 4
A real position
A grid part way through, where the singles have run out. From here the useful moves come from where a digit cannot go rather than where it can.
Finding them systematically
Take a box. List the digits it is still missing. For each one, mark the cells in the box that could take it. If those cells all share a row, or all share a column, you have one.
Two rules of thumb make this fast. Boxes with two or three empty cells rarely produce anything worth having, so start with the boxes that are about half full. And a digit with exactly two homes in a box has a fifty-fifty chance of being aligned — those are the ones to check first.
The same idea in reverse
If a digit’s only homes in a row all sit inside one box, then the box loses it everywhere else. That is box/line reduction, and the two together are usually taught as a pair because they cover the same interaction from both sides.
Running both over every box and line is a complete pass that takes a couple of minutes and very often finishes a hard board without any grid-spanning technique at all.
Other techniques
Try it on a real board
The free board on the home page has a notes mode, which is what every technique past hidden singles needs. Then take the same eye into a live match.