Hidden singles: find the digit's only home
A hidden single is about the whole unit, not one cell. A cell can contain several pencil marks and still be forced if one digit appears nowhere else in that row, column, or box.
Key idea
Choose one digit and find the only cell in the unit that can still contain it.
See the move, step by step
Scan the top-middle 3×3 box for the only possible home for digit 8.
Step 1 of 3
Choose a unit and a digit
Focus on box 2 and look only for digit 8. Several cells are unsolved, so the answer is hidden among a realistic field of notes.
Step 2 of 3
Compare candidate locations
The other open cells in box 2 do not contain candidate 8. R1C6 does, so 8 has only one possible home in the box—even though R1C6 still shows 2, 4, and 6 as cell candidates too.
Step 3 of 3
Place the hidden single
Place 8 at R1C6 and update its peers. The cell did not look solved by itself; scanning the whole box made the placement certain.
Try it on today's puzzle
After every naked-single pass, choose one digit and scan it across each row, column, and box. Hidden singles become obvious when you keep the digit fixed.
Play today