I used a programmable Hewlett-Packard HP-20S scientific calculator in my high school math classes in the early 90’s.
It is still fine and functional here 30 years later and most importantly it is keystroke programmable. A couple of programs I did back then are documented below.
These are my first programs - besides BASIC programming on Commodore 64 and Comal80 in public school on a RC759 Piccoline in the 80’s.
Programs to calculate propabilities for binomialfordelingen
Bestemmelse af nulpunkter
Two programs to find roots (minima) in functions. One using Newtons metode and one using bisektion