If you're addicted to Sudoku, then you'll love this expansion on the game. This is a larger 16 x 16 puzzle comprised of a 4 x 4 grid of 4 x 4 matrices. Instead of merely using the digits from 1-9, EXTREME SUDOKU uses 0-9, A, B, C, D, E, & F - in other words, the hexadecimal digits. Can YOU master such an extreme puzzle?