I had the Hp15c (and still have) but always deeply longed for the hp28s, which was the first to implement a lisp-like programming language in a calculator. Had I bought that one, who knows how different my computing life would have been…

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.

I still have my 28s from the late 80s. Also really rugged except for the achilles heel of a battery door.