Pointing Pairs & Locked Candidates in Sudoku
Locked candidates — including pointing pairs and claiming pairs — are the workhorse eliminations of Hard grids. When a digit inside a box can only sit in one row or column, it is “locked” to that line, so it can be removed from the rest of the line outside the box (and vice versa).
How to use locked candidates, step by step
- Work from full pencil marks.
- Pick a box and a digit, and find every cell in the box where the digit can go.
- If all those cells share one row or one column, the digit is locked to that line — a pointing pair (or triple).
- Remove the digit from that row or column outside the box.
- The reverse — claiming — works when a digit in a row or column is confined to one box; then remove it from the rest of that box.
Pointing vs claiming
Both are “locked candidates”, just pointing in opposite directions. A pointing pair starts in a box: if a digit there is limited to one line, clear it from that line elsewhere. A claiming pair starts in a line: if a digit there is limited to one box, clear it from the rest of that box. Neither places a digit — they erase candidates so pairs and singles appear.
How to spot locked candidates
Scan each box one digit at a time and note whether that digit’s candidate cells line up in a single row or column. When they do, you have an elimination on the rest of that line. They are quick, common, and usually the very next step after Naked and Hidden Singles. See the order of play in tips & strategy.
Pointing Pairs in Sudoku: FAQ
What is a pointing pair in Sudoku?
A pointing pair is when a digit within a box can only go in cells that share one row or column. Because the digit is locked to that line inside the box, it can be eliminated from the rest of that row or column outside the box.
What are locked candidates?
Locked candidates is the umbrella term for pointing pairs and claiming pairs — situations where a digit is confined to the intersection of a box and a line, letting you remove it from the rest of one of them.
What is the difference between pointing and claiming?
Pointing starts in a box and eliminates along a line; claiming starts in a line and eliminates within a box. Both rely on a digit being locked to the cells a box and a line share.