Given are a circle k (grey, metal) and a segment AB (red, metal); AB is parallel to the axis of the circle and its centre P is situated on k (starting position). The plane through the axis of the circle rotates around this axis, and simultaneously AB rotates in this same plane around P so that the angle of the first rotation is twice the angle of the second rotation.

A soon as P has circulated the circle k once, the plane, which is defined by AB and the circle axis, reaches its starting position, whereas the straight AB is rotated by 180° can be mapped to the initial straight AB.

The model shows a one-sided ruled surface, generated by the movement of a straight line. The generating lines are limited by the lateral area of a cylinder, coaxial to the axis of the circle k, and the planes of its two base circles.