Simulation of a mechanical pendulum and representation of the corresponding cylindrical phase surface

The motion of a pendulum can be represented in a phase plane where the time derivative of the angle is put vertically and the angle of the pendulum itself horizontally. Such a phase plane has identical vertical strips which is 2π width. One strip can be drawn on a cylindrical phase surface which is represented by the analog computer. The visible trajectories are drawn in full lines the invisible (on the back of the cylinder) are in dotted lines.