This page is called "zero" because it describes the benefits of tracing the movements of the following toy in your head, and this device is called a "Do-Nothing Machine." The physical toy is for when you feel fidgity and just need to keep yourself occupied and keep the stress down.
Interestingly, one peg describes a Sine Function and one describes a Cosine Function as the handle moves in a circle. The propagating electric and magnetic fields of a light particle can also move in this way. However, what makes it useful for meditators or people who use their minds to solve psychological problems is that when you imagine these motions in your mind with the movements perpendicular and parallel to the ground, or even inside your body, it really calms you down and keeps your mind active without going blank. You can do this inner imagery while having a conversation with another and it keeps the inner thoughts fresh without you getting into trouble shooting off your mouth, etc. It's just a very useful mental thing to imagine for a lot of situations. It makes you better at math and physics, too!