When no further numbers can be discovered scanning stops and from this point it is necessary to use logical analysis. Many players find it useful to help this analysis by marking candidate numbers into the blank cells. These can be divided into two notation types:.

Subscripts

In the subscript notation the candidate numbers can be written in subscript in the empty cells. If the original puzzle is too small to carry this out (most newspapers are printed with cells that are too small to accommodate more than a few digits of normal handwriting) it may be sensible to make a larger copy of the puzzle.

Dots

The other notation is where the player uses a series of dots to represent the numbers 1-9, with 1 being a dot in the top left hand corner of the cell and 9 being a dot in the bottom right hand corner. Using a pencil is recommended as misplaced dots can easily lead to confusion.

When using the marking system a couple of similar rules applied in a specific order will solve any Sudoku puzzle, with no need to backtrack.