Game controls: By default, you play the game with the mouse. Click a box on the grid and select any of the numbers 1-9 or "x" to delete the box or cancel your entry. If you select "Keyboard" in the "Input method" box, you play the game with the keyboard. Use the arrow keys on your keyboard to select a box and type any of the numbers 1-9 on your keyboard. Enable the "Pen Marking" feature to mark the numbers that might go into the box. This should help you solve the puzzle when it's hard!