Locked Candidates
Rated 3.0 on the technique scale · Pointing and claiming.
Locked candidates come in two directions. Pointing: inside a box, a digit is confined to a single row or column, so it can be removed from the rest of that line. Claiming: inside a row or column, a digit is confined to a single box, so it can be removed from the rest of that box.
This is the first technique that does not place anything. It only removes candidates, which is why pencil marks become essential at medium difficulty.
Worth 3.0 points, and usually the first thing to look for when a puzzle stalls.
Locked Candidates — In this box, 5 can only appear in one row 3. That removes 5 from the rest of that row 3.
Practice it: locked candidates shows up most often in medium and hard puzzles. Browse those levels →
How the rating uses it
When a puzzle cannot be finished with easier techniques, the solver applies Locked Candidates and adds 3.0 to the puzzle's score. The hardest technique a puzzle needs decides its level, and puzzles with 26 clues or fewer move up one level.