How to Use Candidates
beginnerUsing pencil marks to track possibilities
Candidate notation (pencil marks) is essential for solving harder puzzles.
Understanding the Concept
Candidates are small numbers written in cells to show which digits are still possible.
Also called pencil marks, possibilities, or notes.
Write all possible numbers (1-9) that could go in each empty cell.
As you solve, remove candidates that become impossible.
When only one candidate remains in a cell, that's the answer.
Candidates help you spot patterns and apply advanced techniques.
Examples
Candidates in Action
Look at the empty cells in box 0 (top-left). Each empty cell shows the possible digits that could go there based on what's already in the row, column, and box.
5
3
123456789
7
123456789
123456789
123456789
123456789
6
123456789
123456789
1
9
5
123456789
123456789
123456789
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Pattern / Involved
Pro Tips
- •Be systematic - fill in all candidates before solving
- •Update candidates immediately when placing a number
- •Look for cells with few candidates first
- •Use candidates to spot hidden patterns
