From bigclivedotcom.

A trackball is like an inverted mouse. You scroll about on your screen by rolling the ball about with your hand. The best types have a patterned ball that is free to spin in front of an optical movement sensor. (I use a Kensington trackball.)

This one is very different from the normal type with optical encoders, because it was designed to work with an existing analogue gaming input to what I would guess was a PC’s 15 pin game/MIDI port.
It was probably intended for games like Missile Command by Atari (which used an optical system in the arcade machines.)

I got this one many decades ago as surplus stock, and I get the feeling it had not proven a success in the area it was aimed at, which I think was gaming. The meshing tolerance of the cogwheels is probably a big factor here. Too tight and they could cause the ball to slip on the rollers, too loose and they wouldn’t mesh properly. Unfortunately it looks like they may have gone a bit too loose on the tolerance.
Keep in mind that this was an era where they didn’t have the same precision 3D modelling CAD we have now.

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