You had a HP-400? I couldn't afford one back in the early 70's (but they were verboten in class, as you said). I had a friend who had one. I remember so well, I was SOOO envious. I don't think I could pick up a slide rule and use it today, as good as I was at using it years ago :-(
That's a good dinosaur test... who remembers sliderules and how to use them lol. Students these days don't even know what sliderules are. I remember paying $300 for my first programmable calculator...
This is beginning to make me feel old... what is it they say... first thing to go is your knees and I can't remember the second thing.