Tutorial

Quick start

1. Fill the grid with 1 to 16, using each number once. Starting clues stay fixed; the final number is bold.
2. Use the shade of the square you are leaving: white means move exactly 1 square, light grey 2, and dark grey 3. Move up, down, left or right. You may jump over other squares; only the square you land on is used.
3. Select an empty square, then use the keypad or type the number. Use Backspace to correct it. Arrow keys move between editable squares.
4. The full grid is checked automatically. Fill Efficiency compares the minimum required entries with the entries you make. Reset clears your entries but keeps the timer and entry count.

The written instructions here cover the essential rules and controls shown in the video.

Finding the next number

Start from a fixed clue. For example, if 1 is on a light-grey square, 2 must be exactly two squares above, below, left or right. Reject positions outside the board or already containing another fixed number. Continue the same way from each number, using its own shade.

You can also work backwards from a fixed clue. Check which possible preceding squares have the right distance to reach it. A finished grid must use every number once and make every consecutive move legal.