In association with the leading Su Doku website, sudokufun.com, this program brings you 15 high quality Su Doku puzzles of varying difficulty. For the uninitiated, these puzzles require only logic to place numbers in a 9 x 9 grid. The only rule is that each row, column and 3x3 box must each contain the numbers 1 to 9 exactly once. True Su Doku puzzles, like the ones this game provides, only have one possible solution. This solution can be reached using pure logic; no guesswork is required at any step. When downloaded, three puzzles are provided for free. When registered this game gives you an extra twelve unique puzzles. Other registration levels give you the ability to download and store more. Pencil marks (used to annotate the puzzles) can be overlayed on top of the puzzle in a transparent layer. Alternatively a different visual mode displays the pencil marks to the right of the puzzle. Please note that although the extra puzzles provided here are not available on the other editions, only one edition of SudokuFun can be run at once.