Sudoku Tips

This tip first in appeared in the Daily Telegraph newspaper, sent in by Sudoku player Brian Thubron:

Recovering from wrong guesses can be laborious with pencil and paper. Here's a tip to get back to the point before the "wrong" guess.

1. Create a blank grid with a spread sheet program such as Microsoft Excel or Lotus 123.
   
2. Fill in the given numbers then save as a new file, say "puzzle1.123", this will preserve your blank.
   
3. I use a large point size font for the given and solved numbers and a smaller point size for the rest. This allows you to insert more numbers in the cell.
   
4. When you get to a point where you have to guess, save the file as another name, eg, "puzzle1x.123" and continue with the puzzle.
   
5. If you come to a dead end, simple load the file puzzle1x.123 and take the other "guess".
   
6. Before changing anything, save the file again as, say, "puzzle1y.123". The reason for saving as another name is that "autosave" keeps the current copy up to date and the file "puzzle1x.123" will be unchanged.
   
7. Each time you need to make a guess, save the file as a checkpoint, to give you a rapid wind-in of the silk!