For those of you that don’t enjoy RPN calculators, you can skip this post… Yes, RPN does stand for Reverse Polish Notation. It doesn’t mean it’s a backwards way of doing things. Actually, it’s a much smarter more compact way of doing things. It was originally just “Polish Notation”, invented by Polish mathematician Jan Łukasiewicz in the early 1900s as a way to represent logic statements without the need for parentheses. Reverse Polish Notation simply means that the operator was moved from the beginning to the end of the statements, so + 1 2 became 1 2 + and the “=” key became an unnecessary vestige. One less button to press!

Although HP didn’t introduce the first ever RPN calculator, they definitely popularized it with their line of calculators. For a fun diversion, you can check out some of the history on the Museum of HP Calculators website.

So where am I going with all of this? Well, I grew very accustomed to the speed and convenience of my HP 42s, which I’ve had for more than 15 years now. I cringed whenever I had to do a calculation on a standard calculator, especially the one that comes loaded by default in Windows. I needed to have an RPN calculator at my finger tips, and thanks to Thomas Okken and the Free42 project, now I do. The image below is an actual screenshot from the Free42 program.

If you happen to be an aficionado of a different HP, there is likely a simulator or emulator available for you. A lot of them are linked on the museum site, including the popular 15C and 41C models. There are really two types of programs out there…

  1. Blank emulators that require you to provide the ROM contents (assuming you own one of the calculators in question). Once set up, these will behave exactly like the original calculator, including every little quirk (and bug) that was in the original. The people providing these solutions cannot post the ROM contents for you or include them in their downloads because they are proprietary code owned by HP.
  2. There are also simulators available that are fully-functional replicas based on a reverse-engineered version of the ROM. These are very good representations of the original, and are much simpler to install and set up. The Free42 program I am using falls in this category.

Well, that’s it. You don’t have to settle for that “backwards” Windows calculator anymore. Go get yourself an RPN!