Quote Originally Posted by Quick Orange View Post
This is kind of off topic, but I've been wondering this for a while now- what's so great about HP calculators? I really like my TI 83, but I'm not nearly as die-hard as some of the HP users I've seen.
Most of the HP fanatics are not tied to HP in and of itself, but to the RPN (reverse Polish notation) style of working with numbers on a "stack." It is elegant in its way and is nice when you need to deal with problems in "stages" and keep track of where you're at.

The stack can contain a bunch of working values vs. most algebraic calculators that only know about the current result or whatever you've explicitly stored in memory.

Prior to algebraic calculators including ( ) parentheses keys, complex problems were difficult to solve without doing it in parts and writing down the parts before assembling at the end. RPN solves that by maintaining intermediate values on the stack.

http://www.xnumber.com/xnumber/rpn_or_adl.htm