How to use Notes
Notes are the leftover digits that still fit a Sudoku cell. Switch Notes on, tap a cell, and mark what is still possible.
Erase a mark when its digit appears in the row, column, or box. When one note is left, that is the digit. Write it.
You do not have to note every empty cell. Note the ones you are watching. A crowded cell with two leftover digits is worth more than a cell you have not looked at yet.
Notes are a help. They are not required, and they are not a score. How to play Sudoku shows where Notes sit in the first scans. Play Sudoku and switch them on when a cell still has more than one legal digit.