Page 30/36 inherited; TurnAngle := TurnAngle + progressTime.DeltaTime * FSpinSpeed; end; The on progress event is different at this level.  ProgressTime  is used to access  DeltaTime. You also have to call inherited directive otherwise the object would not progress at all. To create object defined by this class you would use technique described earlier in this chapter or register the class in GLScene and add it with help of GLScene editor. GLScene beginner's guide, Jan Zizka, 2005