Lesson 3 · Pencil marks
Candidate Notes
Use small candidate numbers to record what can still fit in an empty cell.
See the logic move
Use Next to reveal each reason. On the final step, tap the highlighted cell to complete the move yourself.
Guided solution reveal · Cell Candidates
Step 1 of 3
Focus
row 3, column 7 currently allows 1, 3, 4, 5, 7.
Ask about any cellTap a square on the board
Select an empty cell to see its legal candidates and why the other digits are blocked.
Why this works
- 1
row 3, column 7 currently allows 1, 3, 4, 5, 7.
- 2
Inspect R3C7 and then check its row, column, and 3x3 box.
What the board is showing
TargetThe cell currently being tested.R3C7
Relevant unitThe row, column, or box controlling this move.R3C2, R3C3, R3C8, R7C7
Explain it simply
Candidates are tiny reminders, not guesses. Remove each one only when logic proves it cannot fit.
Step by step
- List numbers missing from the row.
- Remove numbers seen in the column.
- Remove numbers seen in the box.
- Keep only the possible candidates.
Quick check: Should a candidate be removed because it feels unlikely?
No. Remove it only when a Sudoku rule or proven technique blocks it.
Turn logic into skill