The HP28s is amazing. The manual even has a program to convert an algebraic expression to rpn.

In high school it was mind blowing.

But I didn't do anything serious with programming. Normal languages seemed annoying, usr/rpl useless limited as it was to a 4 bit calculator.

Maybe if someone had told me usr/rpl is just lisp. But, it's for the best. I loath computer screens today.