Sudoku Tips: Scanning by Cross-hatching

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.

Two regions contain the number 4 already, and we know that there can’t be another 4 in the same row, column or region.

By crosshatching - mentally putting a line through the rows and columns that already have a 4, we can see where the 4 needs to go in the other two regions.

Now lets look at crosshatching in a full-sized 9 x 9 Sudoku:

By crosshatching the rows and columns that contain the number 5 and intersect the top-right-hand region, you can see that there is only one cell in that region where the number 5 can be placed - the cell colored in green.

Cross-hatching is relatively fast and easy to do, and most people can do it in their heads, without actually drawing the lines.

Its important to scan your puzzle systematically, counting the numbers in each region to identify the missing numbers, then crosshatching for each of those numbers.

Most simple Sudoku can be solved by scanning alone. A 4 x 4 mini Sudoku can always be solved by scanning