1) use a pencil
2) Don’t do any marking up until you’ve solved all of the cells that you can, using cross-hatching
3) Then start to use cross hatching to mark up instances when there are two or three cells in a region where a specific number might go.
4) When you find a solution for a cell, scan the related rows, columns and regions, and delete any pencil marks for that number
Related posts:
- Sudoku Tips: Marking up
- Sudoku Tips: Scanning by Cross-hatching
- Sudoku Tips: Scanning by Counting
- Sudoku Tips: Use a pencil, not a pen
- Sudoku Tips: Find Your Level