great video, I'm also a fan of the guy's other videos (the better toaster and a bunch more)
also learned the interesting connection between the "Ladder Logic" used in that era (and pre computers) and the digital Ladder Logic that I learned on CNC machines when I started in the business years ago (but not EM days, there were no actual relays just the method of programming), and how it originated from these relay stacks and physical hardware and is still diagrammed the exact same way, super cool