In association with the leading Su Doku website, sudokufun.com, this program brings you a virtually limitless supply of high quality Su Doku puzzles. 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. One easy, one medium, and one hard. When registered this game gives you 13 unique puzzles, and the ability to download more of varying difficulty. 20 puzzles can be stored at any one time. 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. All puzzles are solvable by logic only. If you ever feel you have to guess, please see www.sudokufun.com for solving advice. Please note that this edition will not run in conjunction with any other editions of SudokuFun. This edition is identical to the premium edition in every way except this edition can only store 20 puzzles at once.