Lesson 3 · Pencil marks

Candidate Notes

Use small candidate numbers to record what can still fit in an empty cell.

Written and puzzle-tested by Chamara S. Kodikara · Last reviewed 3 August 2026

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

Start wide

This cell could begin with 2, 5, or 7.

What the board is showing

FocusStart here. This is the cell or area being investigated.R5C5

Explain it simply

Candidates are tiny reminders, not guesses. Remove each one only when logic proves it cannot fit.

Step by step

  1. List numbers missing from the row.
  2. Remove numbers seen in the column.
  3. Remove numbers seen in the box.
  4. 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

Practice this technique on a live board

Practice now