Pointing pairs and triples

If every place a number can go inside a box lies on one row (or one column), then that number must sit in that row inside the box. So it can’t appear anywhere else in that row. The candidates “point” out of the box.

How to spot it

1. Pick a box and a number. Mark every cell in the box where it could still go.
2. If all the marks share one row or column, note the line they point along.
3. Remove that number from every cell of the line outside the box.

A real example

In box 9, 6 can only go in r7c9 and r8c9, all in col 9. One of them must be 6, so the rest of col 9 can’t be: r2c9 loses 6.

Tips

• It works with two or three cells. Two is a pointing pair, three is a pointing triple.
• Pointing comes first in most solving orders because it needs only one number at a time.

Practice on Medium puzzles