Difficulty tier T2
Pointing Pairs in Sudoku (Locked Candidates)
Pointing pairs are the cheapest eliminations most solvers routinely miss. They don't place a number, so they're easy to skip — but adding one check for them to your routine unblocks boards you'd otherwise call stuck.
What a pointing pair is
Inside a single box, look at where a digit can still go. If all its possible cells in that box sit on one row or one column, the digit is "locked" to that line within the box. You don't know which cell it is yet — but you know the box's copy of that digit lives somewhere on that line.
So the digit can be erased from the rest of that row or column outside the box. That's a pointing pair (or pointing triple, if three cells).
Pointing vs. claiming
They're the same idea run in opposite directions:
| Type | Digit is confined to… | You erase it from… |
|---|---|---|
| Pointing | one line inside a box | the rest of that line, outside the box |
| Claiming | one box inside a line | the rest of that box |
Both are "locked candidates." Together with naked and hidden pairs they make up tier T2 in Speedoku's difficulty model — the first level past pure singles.
The habit that catches them: after your singles scan, do one pass per box asking "is any digit stuck on a single row or column here?" It takes seconds once it's routine, and it's one of the highest-value additions to a faster solving routine.
Why they matter for speed
A pointing-pair elimination often exposes a hidden single immediately — you clear one line, and suddenly a digit has only one home. That chain (eliminate → single → place) is the rhythm of a fast solve.
Build the habit with reps: practice free, or take today's Daily Challenge.
Frequently asked questions
What is a pointing pair in sudoku?
- A pointing pair (a locked candidate) happens when a digit's only possible cells inside a box all lie on one row or column. Since the digit must come from that line within the box, it can be erased from the rest of that row or column outside the box.
What's the difference between pointing and claiming?
- They're the two directions of locked candidates. Pointing: a digit is confined to one line inside a box, so you erase it from the rest of that line. Claiming (box-line reduction): a digit in a row or column is confined to a single box, so you erase it from the rest of that box.
Why do I keep missing pointing pairs?
- Because they don't place a digit, so beginners scanning for placements skip right past them. The fix is to add one check to your routine after singles: for each box, ask whether any digit is locked to a single row or column, and make the elimination.