Face off with a master. Don't settle when it comes to your Sudoku: Serious Sudoku lovers choose puzzles hand-crafted by Nikoli, the Japanese company that invented the game. Every puzzle in this calendar is hand-crafted by the best Sudoku makers in the world--not from a computer--to balance toughness and solvability and keep you hooked. The week begins with the easiest puzzles and the difficulty increases day by day. Just in case you need them, solutions are printed on the back of the pages. Printed on responsibly sourced paper and 100% recyclable.