Pointing Pairs
If all candidates for a digit inside one 3x3 box lie on the same row or column, you can remove that digit from the rest of that row or column outside the box.
Cell references use A-I / 1-9 coordinates. For example, A2 means top row, second column.
Checklist before elimination
- You are analyzing one specific 3x3 box.
- All candidates for one digit align on one row or one column.
- The same row/column still has that digit outside the box.
Steps
- Choose one box and one target digit.
- Check whether candidate cells align to a single row or column.
- Eliminate that digit from the same row/column outside the box.
Real solve checklist
- Select one box and one digit only.
- Verify alignment on exactly one row or one column.
- Eliminate only outside-box cells on that same line.
The biggest mistake is extending elimination beyond the aligned line.
Concrete example (valid)
In the top-left box (R1-3, C1-3), digit 5 appears only at R1C2 and R1C3. That means 5 must stay on row R1 inside this box.
Candidate 5 is locked to row R1 inside one box, so row R1 candidates outside the box can be removed.
Difference from Claiming
Pointing starts from a box and projects into a row/column. Claiming starts from a row/column and projects into a box. They are sister patterns under Locked Candidates.
Invalid case (do not eliminate)
If the same box has candidate 5 at R1C2 and R2C3, they are not aligned in a single row or column, so Pointing does not apply.
Candidates are split across different row/column lines, so Pointing Pairs is not valid.
Common mistakes
- Judging by candidate count instead of alignment.
- Eliminating beyond the target row/column scope.
- Applying elimination before all box candidates are verified.