Ha! These were a kind of special terminal, they were essentially dumb terminals not much different than what you might find at an airport ticketing terminal. In other words, they were a "data telephone". They had the ability to call up the server, download 1-2 pages of something, edit that something, poop it out sideways to a printer or a plotter, and poop it back to the main server, updated. Ahh, but these had a modicum of graphics capability. They were used in early CAD/CAM applications is the easiest way to picture what they could do. When these were around, they were just about the only game in town. There were no PCs, certainly not with any graphics capability at that time.
As it turned out, they became the terminal of choice for an astounding variety of early computer systems. Dow Chemical for example ran their refineries on them, because they could display bar-graphs of several temperature/pressure nodes. Blue bar red bar green bar yellow bar, semi-skilled technician makes sure the bars are all within a range so the refinery doesn't blow up. Applied Materials used these to do about the same thing on their semiconductor furnaces. BART, Bay Area Transit System ran their trains using the things. My customer list was like the Fortune 100. I did deals with Hughes satellite which happened to be in the next town over from where I lived that were top-secret...I had to deliver the terminals to a guy with a metal cart in the parking lot. Everybody thought that was pretty funny.
All these terminals were in the "4xxx" series and had various screen sizes, but the 4205/4207 13" screens were the most common, the most bulletproof, and the most profitable.
My business effectively ended when I determined that I had found all of these terminals in the entire world that were not either in use, in some dealer's inventory priced too high for me to buy, or, in FInland. Not kidding. I effectively found every one of these that was available for sale in the world and put myself out of business, LOL. I could probably sell them today if I could find them, 10 years later. Keep in mind, you cannot buy just one: You have to buy them in clusters so that if one or two break to where you can't fix them, you still have 5 more to sell.
Best business I was ever in, by a factor of 10. And by the way, I knew all the guys and purchasing agents at Tektronix so that when an end user called up needing a used terminal which they didn't have (because they were buying them from me) Tek would refer them to me. For a year or two, I was the God of Tektronix terminals & had the Fortune 100 by the short hairs.
You have to remember, that these terminals were used as "dashboards" for much more expensive systems. When a $1.2 million Applied Materials semiconductor furnace that made $50,000 worth of chips every day was down because the Tek terminal that showed what temperature, what pressure, how much Silane, etc; was fried, let's just say they didn't mind paying Federal Express to get the $850 replacement terminal to them.