Rather than posting the entire post again, I would like to link one of my old purchases. It's a VERY EARLY E Heuer, actually made when E Heuer, the original company owner, was still running the company. Now known as Tag Heuer.
The watch does work, and I can't figure out why, when clearly there are parts to it, but maybe they were to another watch? Have no idea.
Check it out there.

Original old Hallmarks are listed and on the watch movement.

https://ihc185.infopop.cc/eve/forums/a/tpc/f/2291010082/m/1681058681

trademark