Click a cell for a row+column cross to the edges. If the cell shows a digit, all matching digits highlight and the full 3×3 box is shaded. Given clues are dark; your entries are lighter blue. Completed number buttons hide. Pencil marks may repeat in a row, column, or box until you enter the correct digit in the right cell—then that digit is removed from pencils in that row, column, and box. P pencil · E/M/H easy/medium/hard · digits to enter · Backspace erase.