HP calculators were an important part of my formative years. I have a 12C, 15C, and 16C (all original models). I also have an HP-35 (red LED digits) within reach right now. That was the calculator I used for high school exams, because we weren't allowed "programmable" calculators so I had to go a bit retro for the time.
The 16C was an interesting model. It had a lot of potential capability with the different word sizes and bitwise operations, but I think it fell short in practice because the operations it could do just weren't that useful.
My favourite model is the 15C, it got me through four years of math, physics, and computer science university classes. The integration and matrix functions were super useful because it was hard to do some of that stuff in your head.
MajorBBS could handle multiple lines on its own, but you had to handle ALL of the lines with one box. That meant a serial port interface like DigiBoard which provided some number (8 or 16 or more) of serial ports that you would connect to modems.
I've done AoC on what I call "hard mode", where I do the solutions in a language I designed and implemented myself. It's not because the language is particularly suited to AoC in any particular way, but it gives me confidence that my language can be used to solve real problems.
The 16C was an interesting model. It had a lot of potential capability with the different word sizes and bitwise operations, but I think it fell short in practice because the operations it could do just weren't that useful.
My favourite model is the 15C, it got me through four years of math, physics, and computer science university classes. The integration and matrix functions were super useful because it was hard to do some of that stuff in your head.