This is an attempt to simulate this type of harmonograph, consisting of a pen attached to a horizontal bar which is suspended on two wires. This can be modelled as a single pendulum with an oscillating twist.
As in the three-pendulum harmonograph simulation, the 'scene' shows a top view of the harmonograph, and the 'settings' let you change its parameters, in this case the pendulum motion, twist and the position of the pen along the bar.
