Pendulum Toy; G. E. Worthington, 1932
This device has two pendulums that rotate in a single plane (a Lissajous figure drawing machine). The point where the pen arms connect can be changed, but this adjustment only effects the skew of the drawing and really isn't very useful. A much more valuable adjustment is the ability to easily change the length if the pendulums by raising or lowering the pendulum weights!
The planes of rotation of the two pendulums should be adjustable (or set at a 90 degree angle of opposition), in my opinion; this setting produces the classic family of "pure" Lissajous curves.Click on an image to view full sized -