Good old trackball, one of the first ones with the buttons finally relocated to the below the ball position. In the 80-90 it was one of standard trackballs widely used for various computers, as well as with industrial and medical equipment. Calculated resolution is 192 PPR / 30 CPI.
Traditional 5-bearings design, with fine NHBB R-2ZZ stainless ball bearings. Fortunately they're of serviceable type, so removal of shields for cleaning and lubrication change was easy job.
Interesting thing is - free spinning of the ball, typically appreciated by users, is artificially suppressed here: teflon felt ring is glued inside ball's opening. Obviously, it was initially designed for industrial applications where vibrations cause unwanted movement, and dirt particles could contaminate device internals. I've removed it.
Switches resemble keyboard ones, having significant amount of travel unlike common Omron-type ones. For Macintosh computers, two-button variant with extra wide primary button (taking space for both left and middle buttons in standard 3-button model) was released. Travel is not straightly downward: there's pivot point, so the key cap moves at some angle.
Was manufactured with many different output standards: quadrature, ADB, serial, but most interesting among them was keyboard interface. Device was connected in between of keyboard and PC, intercepting keyboard signals and injecting its own ones. From PC 'point of view', all the data looked originating from keyboard - so it was possible to use it on the machines without dedicated pointing device port, and free up valuable serial port(s) for another peripheral connections. The same keyboard was used to program the trackball, capable to store some key scancode sequences as a macros, and repeat them later at the press of button. Ball movement, in particular, produced arrow keys codes for up, down, left & right cursor movement, as if the user have used ordinary keyboard for navigation.
There were also variants with contact encoders instead of optical shutter discs. Some models were equipped with 8-pin RJ-45 connector and detachable cable.
December 1983 Byte magazine and in German November 1982 Computerwoche article.
Many rebranded variants are known: Honeywell, Dynapar, PGT MicroTrac, Cognex, Teknar, Mentor, Finnigan Mat, Foxboro, Asher... My sample was bought as "Foxboro P0500ZG". Some of labeling samples I'm aware of:
https://trackballs.eu/media/DiscInstrum ... /LX200.pdf
Advertising and reviews from 1985 - 1988:
Conversion to USB was relatively simple, with some minor exceptions. Bearings were fixed with glue, and in addition covered with plastic part, also glued. With PCB board glued to the case, it's an "unfriendly" design for repair or modding. Separation of PCB caused mounting pins destruction, so I've fixed the board by self-taping screws. Glued ball retainer is now pressed by piece of rubber affixed to the inside of cover. The case have plenty of room in the flat wrist-rest part, so it's easy to put mouse controller PCB with E-Cmos EC3592RS chip there. USB converter I've placed at the cable exit.
After using USB-modded version for a while, I'd say this trackball is nice. The case is very convenient: lowered prolonged part is used as a wrist rest. Movement of the ball is quite smooth, click feel is soft and very pleasant. Location of buttons is not perfect: excessive bending of thumb and fingers required to actuate them without removal of control fingers from the ball - but anyway, it's a significant progress over early trackball designs with buttons above the ball, where one-hand simultaneous clicking and movement (drag operation) was nearly impossible.
As usually, this trackball was actually used to prepare this article.