Looks like they used an even smaller ball. I didn't know 38mm pool balls were a thing... > To be able to call this a trackball, we also need some kind of ball

Looks like they used an even smaller ball. I didn't know 38mm pool balls were a thing... > To be able to call this a trackball, we also need some kind of ball or sphere of course. Many people go with the smallest regulation billard balls with a diameter of 38mm.