A spiral spring made of cold rolled steel is clamped between a ball bearing mounted shaft and a fixed bracket. Two levers are fitted to the shaft diametrically opposite each other. Two sliding weights of metal on the levers can be securely fixed in position using clamping screws. These form the rotating mass with an adjustable moment of inertia.
The system is displaced by hand. The angle of rotation is read off on a 1° scale disc that is also attached to the shaft. The unit is intended for wall mounting.