Hidden Single
Level: Basic
Confirmed when a number can only go in one cell within a unit.
A Hidden Single occurs when a specific number can only go in one cell within a row, column, or box. Even if that cell has other candidates, it's confirmed as that number.
For example, if the number 7 can only be placed in one cell within a box, that cell becomes 7 regardless of its other candidates.
It's less obvious than the Naked Single, but counting where each number can go within a box makes it easy to find — a key skill for beginner and intermediate solving.
Related Techniques
Basic
Naked Single
When only one candidate remains in a cell, that number is confirmed.
BasicPointing Pair
When a box's candidates for a number align in one line, remove that number from the rest of the line outside the box.