You're trying to find missing digits in blocks, rows, or columns but are stuck. For instance, if it looks like it could fit in the cell, and you see 1, 2, and even 7, we suggest using the note method. This lets you indicate the numbers that might fit in the cell.
If you're working on a Sudoku puzzle on paper, you can make notes in pencil and then erase them. Or, you can make your notes with a pen, just lightly touching the paper. As an alternative, you could put small numbers in the corner of the cell to avoid any potential distractions down the line.
If you're solving Sudoku on our website or mobile app, you can use a special mode to make notes by clicking the "pencil" button. Let's look at an example of using the note mode. Have a close look at the image below:
- which values are already in the central 3x3 block: 2, 4, 6, 3 and 7;
- which numbers are missing in the block: 1, 5, 8, and 9
- turn on the note mode and write: 1, 5, 8 and 9 in the empty cells (see the picture below);
- which numbers are in the row (3, 6, 7, 4);
- which numbers are in the column (8, 9, 2, 3, 1).
If we eliminate all the other possibilities, we're left with a five as the only possible digit in the intersection cell (the one with the orange frame). So we turn off the note mode and just write in the cell the number five.
Using notes on the Sudoku game board is a pretty advanced technique. It's typically used to tackle tough Sudoku puzzles, as well as those at the Expert and Guru levels.