Orbita oscillating winding. The oscillating winding action of the SPARTA winder is totally self-regulating and there is absolutely no chance of damaging an expensive watch by over-winding. A semi-circular rotor, attached to the back of the mounting cup, is the "heart" of the patented ROTORWIND® system. Made from a dense, non-magnetic iron material, it is supported by two free-turning precision ball bearings, thus enabling the heavy mass of the rotor to produce the "back and forth" motion when the cup is raised and then released from the 12 o'clock position.