In 2008 I was in high school and wrote a TI-BASIC tutorial in German [0] on my blog that became by far the most popular thing I wrote - maybe on par with my post about how to fix a quest bug in Skyrim by teleporting Delphine.
I was a bit mad back then that people for some reason appreciated those posts more than many very deep teenager ramblings about politics/philosophy :D
There‘s HP calculator guys and TI guys. Around the age of 17 I spent lots of time programming my HP28s calculator in a Forth like language that had symbolic mathematics, lots of ideas from Scheme (closures, functions as first class arguments, recursion). It felt like magic dealing with concepts I hadn’t seen in the C compiler on my Amiga or later in Turbo Pascal. But I saw these concepts later in Mathematica and was familiar.
I had programmed games, complex 3d visualisations (super slow but oh well), and was totally fascinated by what this device could do.
An HP 50g was my calculator of choice, and the whole RPN style really rubbed off on me. Plus it had more advanced symbolic algebra capabilities than a ti83 equivalent. I enjoyed learning common lisp, scheme, racket, etc through high school and college and still am fond of them today because of this calculator.
Most if not all high schools and colleges in the US required TI “graphing” calculators for algebra/trig on up. I don’t know if they still do. I never saw this HP28, sounds awesome!