More Tips for Marking Up Sudoku

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