Slightly more complex than the UI of something like GNU Emacs, but with a better user interface. Keep in mind that not that many machines ever existed, I would

Slightly more complex than the UI of something like GNU Emacs, but with a better user interface. Keep in mind that not that many machines ever existed, I would think around 10000 -> thus the UI was less polished, but more capable. It's definitely more difficult, because it does not look&feel like common other user interfaces (say, the Desktop Metaphor used by Apple and others), plus it lacks a few decades improvements.