Mode:Input modes - shortcuts: Z, X, C & VEnter a digitAdd an "outer" pencil-mark - Shift+DigitAdd an "inner" pencil-mark - Ctrl+DigitColour cell background, double-click to clear123456789DeleteDelete digits, pencil-marks & color highlightsCheckCheck grid for conflicting digitsUndo last change - Ctrl+Z or [Redo last change - Ctrl+Y or ]Restart the puzzle