Trammel of Archimedes

This mechanism consists of a base with two slots intersecting at right angles. Two sliders are confined within the slots and are attached to a handle by pivots (screws) at fixed positions along the handle. The mechanism can be used for drawing a perfect ellipse. This is done by positioning a writing utensil at the end of the handle while making a full revolution.

With that said, it is often sold in novelty shops with interesting names like Bullsht Grinder, Bullsht Masher or Do-Nothing Machine. Interestingly, most of the names are preceded with state names such as Arkansas, Kentucky, etc. I guess that’s how locals make fun of their neighbors.
More Info / Build Instructions: https://www.instructables.com/id/Trammel-of-Archimedes/
Animation: https://youtu.be/NiEOJxK4AYA