Notes are the small digits you write in an empty cell to list what can still go there. On easy puzzles you can skip them. From Hard upward you cannot: the techniques that finish those puzzles are patterns in the notes, and without notes there is nothing to see.
When to start writing them
- Easy — no notes needed. Every cell falls to a plain look along its row, column and box.
- Medium — still possible without notes, but you start asking where a digit can go inside a box instead of what goes in a cell.
- Hard and above — write them. A naked pair is two cells whose notes are the same two digits; you cannot spot that from the clues alone.
Two ways to write them
Full notes. Every empty cell gets every digit that is not yet ruled out. It is complete, and every technique can be read from it, but on a fresh puzzle that is well over a hundred small digits to write and keep up to date, and one slip is enough to mislead you.
Two-cell notes. Go digit by digit through each box and write a digit only where it has exactly two possible cells in that box. You write far less, and what you write is the useful part: two such marks side by side in a row already tell you where that digit goes in the row.
A practical order is to start with two-cell notes while singles are still coming, then fill in full notes for the cells that remain once you get stuck.
Keeping notes honest
- When you place a digit, remove it from the notes of every cell in the same row, column and box.
- Write a note only after checking all three: row, column and box. A digit that is already in the box does not belong in the note, even if the row allows it.
- When a note leads to a surprising conclusion, recheck the cells it came from. A wrong note is worse than no note — a pair built on it points you to a wrong answer with full confidence.
What to look for in them
- Naked pair — two cells in one row, column or box whose notes are the same two digits. Those digits can be erased from the rest of that unit.
- Hidden pair — two digits whose notes appear in only the same two cells of a unit. Every other digit can be erased from those two cells.
- Pointing pair — inside a box, every note for one digit sits on the same row or column. That digit can be erased from the rest of the line outside the box.
Notes in this game
- Press the Notes button (the pencil), or the N key, to switch to notes. Tapping a digit then adds it to the cell, and tapping it again removes it.
- Placing a digit clears it from the notes of the cells it sees, so you do not have to.
- Auto notes in settings writes full notes for every empty cell and keeps them current as you play. A note you erase by hand stays erased.
- From pairs onward, a hint often ends by erasing notes rather than placing a digit. Those erased notes stay gone as well.