Exhibit: Harmonograph

Set both pendulums swinging and press the button to lower the pen.

The pendulums have different lengths; the long one which carries the pen completes two swings in the time that the shorter pendulum (which carries the table) completes three swings.

As the pendulums swing, they lose energy and so they swing less and less. This makes the patterns drawn by the pen get smaller and smaller, and fills in the gap that would otherwise be in the middle of the pattern.

The times of swing of the two pendulums are not quite in the ratio of
three to two. This means that the pattern does not just repeat itself as
the swings get smaller, but also rotates. This is the final twist to make
the patterns really artistic!