Hidden Single
Rated 2.6 on the technique scale · A digit with only one home in a unit.
A hidden single is a digit that can only go in one cell of a row, column or box — even though that cell may have several candidates.
The trick is to ask the question per digit rather than per cell: "where can the 7 go in this box?" If there is only one answer, the 7 goes there, and every other candidate in that cell disappears.
Hidden singles are worth 2.6 points. They are the reason a puzzle with plenty of clues can still be solved without notes.
Hidden Single — In this row 9, 5 can only go in one cell, so it must go there.
Practice it: hidden single shows up most often in easy and medium puzzles. Browse those levels →
How the rating uses it
When a puzzle cannot be finished with easier techniques, the solver applies Hidden Single and adds 2.6 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.