This wobbly spinner also called a "rattleback" features a physics defying unpredictability. Which makes it perfect for equally unsure decision making. Includes one 3¾" long rattle back and one 4½" wide decision disc.
This mechanism demonstrates a surprising way to generate an ellipse by using a four-bar linkage. The shape of the ellipse can be defined by the path the intersection point of the two crossing bars follows. This fact is analogous to another neat way to make an ellipse with two fixed foci and a string of fixed length attached to them.