Internals of early mouse supplied by Symbolics (Mouse House: Hawley X063X mark II)

A piece of precision engineering, note twin commutators and brushes. It still works as well as any modern mouse - the solid steel ball and ball bearings have a momentum and feel which can make tracking different in pleasant ways. They are able to take quite a beating and for maintenance just need accumulated fluff to be removed from the roller balls.

Bases of 2 mice: Hawley X063X Mk II