Sudoku pencil marks: noting the candidates
Pencil marks are the small digits that list every candidate for a Sudoku cell. Learn how they help you spot singles and pairs in harder puzzles. Solving techniques · lesson 4 of 7.
The lesson in words
In harder puzzles, write the candidates (the digits a cell could still be) as small pencil marks. The game’s notes button does this.
Here every empty cell shows its candidates.
With notes on, naked singles jump out: a cell with only one small digit.
Try it: Tap the cell in row 3 that has only one candidate.
Notes turn hard puzzles into patterns you can see. Next: naked pairs.
Questions
You fill in a 7. Which pencil marks should you update?
Remove 7 from the notes of every cell in the same row, column and box. Those cells can’t be 7 any more.