How to Use Pencil Notes in Sudoku
Pencil notes, also called candidates, are the small numbers you write in a cell to remember which digits could still go there. Used well, they turn a stuck board into a list of clear next moves.
When to start writing notes
Do not start with notes. First fill every hidden single you can find by scanning each number from 1 to 9. Notes are most useful once the easy numbers are placed and fewer candidates remain.
How to write them
- For each empty cell, write every digit that does not already appear in its row, column or box.
- Keep a fixed position for each digit (1 top left, 9 bottom right) so a glance tells you which are there.
- Work box by box so you do not miss cells.
Keep notes clean
The moment you write a number in ink, erase it from the notes of every cell in the same row, column and box. Stale notes are the main reason people make mistakes late in a puzzle.
What notes reveal
- Naked single: a cell with only one note left.
- Hidden single: a digit that appears in the notes of only one cell in a unit.
- Naked pair: two cells in a unit with the same two notes.
In Inkdoku, turn on Notes and tap numbers to pencil them in. Notes are drawn in a darker grey so they stay readable, and writing a number in ink clears it from the notes in the same row, column and box automatically.
FAQ
Do expert players use notes?
Most do on harder puzzles. Even experts pencil in candidates once the obvious numbers are placed.
What's the difference between notes and answers?
Notes are possibilities; an answer is the one number you are sure of. Keep them visually different so you never confuse the two.
Can notes be filled in automatically?
Some apps do it, but writing them yourself is how you learn to spot patterns. Inkdoku clears notes automatically but lets you write them.