In this example, we introduce the first custom widget that can paint itself. lcdrange.h contains the LCDRange class definition . ... This file is very similar to the lcdrange.h in chapter 7. ... CannonField inherits QWidget and we use the same idiom as for LCDRange. int angle() const { return ang; } public slots: void setAngle( int degrees ); signals: void angleChanged( int ); . ... This will update CannonField's angle value whenever the user operates the LCDRange. ...