I love how most of the HP calculators produce the same result, even between ones with different processors. This is because it uses an internal interpreted language, SystemRPL, to do most of its complex and trigonometric math functions. As long as the simple interpreter is correct, handling complex math functions is portable between models.

http://www.hpcalc.org/hp48/docs/programming/

I'm a vintage calculator collector and I love to see this topic getting featured on HN! If anyone has any questions about vintage calculators just ask.