Like the standard Sudoku, this Sudoku consists of a grid of nine rows and nine columns subdivided into nine 3x3 subgrids.

Like the standard Sudoku, it has two basic rules:

1. Each column, each row and each box (3x3 subgrid) must have the numbers 1 to 9

2. No column, row or box can have two squares with the same number.

The puzzle can be solved with the help of clue-numbers which are small numbers written on the intersections between two cells. Each clue-number is the product of the two digits in the two cells that are on either side of it.

For example, 8 in the top right box means that possible pairs of numbers for the cells above and below are either 1 and 8, 8 and 1, 4 and 2, or 2 and 4 respectively.