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.

The more difficult Sudoku puzzles can’t be solved just by using the scanning techniques of crosshatching and counting. In these more complicated puzzles, scanning will still leave you with cells where you don’t know which of two or more numbers to choose.

The most simple scanning technique is counting - select a row, column or region, and count the numbers in the cells in from 1 to 9, to identify the missing numbers.

Of course, this is most helpful when there is only one number missing from the row, column or region that you’re counting - then you know that number belongs in the missing blank cell.

Scanning techniques involve running your eyes over a row, column or region.

Cross-hatching is the scanning of rows and columns to identify which cell or cells in a region might contain a specific number.

Check out the mini Sudoku on the right.

Each row, column, and region of four cells must contain the numbers 1 to 4.