Lesson 6 · Beginner technique
Hidden Singles
Find the only cell in a row, column, or box that can hold a particular number.
See the logic move
Use Next to reveal each reason. On the final step, tap the highlighted cell to complete the move yourself.
Step 1 of 3
Focus
5 has only one legal home in row 3: row 3, column 7.
Select an empty cell to see its legal candidates and why the other digits are blocked.
- 1
5 has only one legal home in row 3: row 3, column 7.
- 2
Inspect R3C7 and then check its row, column, and 3x3 box.
What the board is showing
Explain it simply
The answer is hidden among several notes, but that number has only one home in the group.
Step by step
- Choose one row, column, or box.
- Pick a missing number.
- Mark every cell blocked for that number.
- Fill the one legal cell left.
From demonstration to independent solving
Prove the move yourself
What you should be able to do
Find a digit that has one legal position in a unit even when the target cell still shows several candidates.
Read the exact board evidence
In row 3, several empty cells retain multiple notes. Candidate 5, however, appears only at R3C7 after column and box restrictions are applied. Other notes may remain in R3C7, but 5 has nowhere else to go in the row.
When the logic is strong enough
A Hidden Single proof names both the digit and the controlling unit, then demonstrates that every other empty cell in that unit rejects that digit.
Train the pattern without guessing
Select one incomplete row and count the locations for each missing digit. Do not study one cell at a time; search for a digit whose location count is exactly one.
Quick check: Can a Hidden Single cell still contain several candidate notes?
Yes. One candidate is special because it appears nowhere else in that unit.
Turn logic into skill