The Casio fx-6300g graphing calculator has a subtle bug that affects using certain comparison operators against array memories, which will effectively cause the two sides of the comparison operator to be swapped. Here's how to trigger the bug, and what you can do to avoid it.
I bought an old Casio fx-6300g graphing calculator from ebay (it's so tiny!), and couldn't find many programs written for it. Who would imagine that the internet wouldn't be awash in programs for an obscure, low-end calculator from 27 years ago? So, I wrote a few: prime factors, binomial probability, and negative binomial probability.