Strategy

Sudoku notes and pencil marks

Notes are the single biggest step from beginner to intermediate solver. Used badly they clutter the board. Used well they make hard puzzles easy.

What notes are for

A candidate is a digit that could still go in a cell. Notes record them, so you do not have to hold dozens of possibilities in your head. Every technique beyond singles, from naked pairs to X-Wing, is read from the notes.

When to start writing them

On an easy puzzle, do not. Singles are faster without notes. Start when you have scanned for hidden singles and naked singles and nothing is left.

How to write them well

1. Go unit by unit. Fill the candidates of one box, then the next, so you do not forget cells.
2. Always put each digit in the same spot within the cell: 1 top left, 2 top middle, 3 top right and so on. Then you can read patterns at a glance.
3. Cross out a digit in all peers as soon as you place it in a cell: its row, column and box.
4. Never write a candidate you already know is wrong.

Full notes versus partial notes

Some solvers write only candidates for cells with two or three options. That is faster but loses information needed for hidden singles and fish. Full notes are slower to write but safer. Our web board and the app can remove notes automatically when you place a digit, which keeps them accurate.

Common note mistakes

• Forgetting to update notes after a placement. This is the cause of most wrong eliminations.
• Making notes in some cells but not others, which hides patterns.
• Writing them too large to read. Keep them small and neat.

Try it

Open the game, turn Notes on and play a Medium puzzle. See how pairs and pointing pairs appear once the notes are written.