Very easy Used at every level, from very easy puzzles up.
Hidden Single
A digit with one place left in a unit
Turn the question around: instead of asking what a cell can hold, ask where a digit can go.
Every row, column and box needs each digit once. When a digit has only one possible cell left in a unit, it goes there, even if that cell has other candidates.
With the candidates shown, it is a digit that appears only once in a row, a column or a box.
What to look for
Pick a digit and a unit, and count the cells that can still hold it.
Example
- The cell it fills, with its digit in green
Practise it
In the app, Learn › Hidden Single sets exercises on real positions, then a full puzzle that needs this technique and nothing harder.