What Ever Became of…Reverse Polish?


When I was in jr. high school, I participated in some calculator skills type competitions. We got these weird HP calculators that used something called Reverse Polish notation. Although I imagine many of you are at least relatively familiar with the concept, here is the not at all confusing explanation from Wikipedia: “Reverse Polish notation (RPN) is a mathematical notation in which every operator follows all of its operands, in contrast to Polish notation, which puts the operator in the prefix position. It is also known as postfix notation and is parenthesis-free as long as operator arities are fixed.” (Wikipedia)

Mostly, I just remember that you plugged things in a different order, and if you practiced you could be fast at doing the maths. Then you would get to the competition, and there would be a couple of girls of a certain non-stereotypical nationality that would get through three times as many problems as anyone else. Either way, where have these oddball notation calculators gone? Are they still around in certain circles? Do you use one at work? Whatever happened to Reverse Polish notation?

Image from, via

  • I'm still fond of my HP-28S, but I've noticed over the last few years that fewer of my students have calculators at all. They're satisfied with whatever comes with, or can be installed upon, their phones, tablets, and the like. So, unless I want to take a close look at their screens, I can't easily tell what method they're using just by seeing their devices. I suspect it's seldom RPN, though.

  • I still have one somewhere, probably a 12C from my days teaching Business Statistics, but I haven't used RPN in twenty years. Like Harrell's students, I just download the needed app to my phone.

  • Nuclearspork

    Certain groups still use them, mainly scientists cause it is still faster but I'd say now adays its rare to have math problems I have to do that I need a calculator for.

  • skitter

    I deliberately buy TIs with the same interface so I don't have to rewire myself when switching between calculators. Though for some reason I was thinking about RPN just the other day.

  • Tiller188

    I sort of wish I had learned RPN (Dad had/has calculators that use it and is very handy with it), but I never did, partly because I think its benefits are somewhat reduced now. From what I remember and understood, the concept of the "stack" on an RPN calculator was very handy for performing sequential operations without having to worry about order of operations mixups (the classic (1-2)*3 vs. 1-2*3). Ever since the advent of graphing calculators with more memory and multiline/higher-res screens, though (such as the type that were getting common by the time I was in high school and regularly using a calculator), it's been pretty easy to see on the screen exactly what equations had been entered and solved, and also to go back and retrieve a previous result to use in another calculation. It's still clunkier and less efficient than RPN to someone who knows how to make good use of it, I'm sure, but I feel like there's also less memory/guesswork than keeping track of the stack mentally. As far as the smartphone deal goes, it's nice to have the equivalent of a one-line scientific calculator in my pocket at all times (use it for checking gas mileage every time I fill up), but I still use my college-era TI-89 at work for exactly the benefits mentioned above.

  • windbuechse

    <img src="; width="600">
    In high school, I was the top mathlete in our division and received a Pickett vector-log-log slipstick as the award. The next year, 1973, the winner received a HP-35 calculator which were ~$700 IIRC. Man was I pissed. I couldn't afford a scientific calculator until my junior year of college. However, I was faster on the slipstick for most of the work.
    <img src="; width="600">
    I finally got a NOVUS (National Semiconductor) calculator and later, a copy of this book. By then I had access to a PDP-11 and soon graduated. For some reason, I've never needed that skillset in dentistry….

    • That last line brought back memories.

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      • windbuechse

        Think I'd keep that figurine out of my patients line of sight….

        • Metric Wrench

          Mathlete competitions – I had wiped those from memory! Yeah, the prize at our statewide was a 20 dollar savings bond. An HP would have been much more useful!

          I was such a misguided youth, I figured I'd do the Mathlete and JETS competitions to meet girls. Yeah, I know, if you're hunting for elephants go where the elephants are… But even at 16 I was looking for a chick with brains. Dang if I didn't find her – met me wife at a JETS competition, hitched up 5 years later, still married due to both calculating a positive cost benefit ratio. Oh – and she drives a HP-35.

  • Metric Wrench

    I grew up in the HP 41 era – I inherited me brother's HP-41C when he hit grad school and stepped up to the 41CX. At the time, my school didn't require (or teach) any one particular calculator, so the 41 vs TI 55 debate was running rampant. I even had the poster – a picture of a dorm with one window lit, with the caption 'not everyone has an HP yet'.

    I still use it today – it is set up at me left hand, above the left handed mouse, ready for quick calcs whilst the right hand is free to operate the phone and notepad. Old habits die hard. But, I must say, I only use it for quick calcs – I don't really use the stack or the expansion modules anymore. That stopped back with Quattro – which I still carry a torch for rather than Excel.

  • Every time I reverse Polish anything it ends up all dull and lacklustre, like it was sprayed with silver Christmas Tree paint rather than being chromed at the factory.

  • ˏ♂ˊ mzs zsm msz esq

    Carly is what happened to RPN, it hurts too much to think about, so I'll stop. It's also not totally fair but the details are boring.

    Anyway, one of my parents' friends worked at HP (same guy that helped my dad chop down a Christmas tree, he was a good man), The summer before 5th grade he bought me an 32S (with an employee discount, but still that was amazing), and I was never the same after. The neat things about it was that it was programable and the documentation was incredible. I learned about things like integration and you could even solve them numerically, that was so neat for me as a little kid seeing that line-up with geometry.

    Later I had 48S (someone stole that) and 48G (and eventually that chewed-through batteries). At that point the replacements had terrible keyboards so I started using numpy (see the way you programmed the things by that point it was this syntax something between lisp and forth with like the power of mathematical lite or something behind it and it was fantastic for quickly running through ideas). My fantastic wife got me a 50G or something like that a few years ago. It was almost as good, but little things like if you did not press the key just thte right amount you might register zero or two key presses instead, plus the battery life was not all that great. It's still almost indestructible like the others but the documentation was terrible. Anyway by then numpy was the go to and I don't use it much.

    Oh and the description of RPN, so basically it's saying it was like this:

    3 ENTER
    2 +

    Polish would have been like:

    + ENTER
    3 2

    The arity stuff, that's cause there are things like lisp out there:

    (+ 3 2 1)

  • Slow_Joe_Crow

    I think the schools got onto the TI bandwagon with algebraic notation being easier to learn. I still have an HP48-G from 1995ish and I run the Droid 48 HP48G emulator on my smart phone in honor of it.

  • I'm late to the game, but it's still around. You can buy a RPN H-P 12C Financial Calculator at Staples or Wal-Mart or Amazon.
    <img src="; width="450">
    Here's a great WSJ article about the 12C from 2011:
    Wall Street's Cult Calculator Turns 30

  • I use RPN daily. I did switch away from my beloved HP 33s to a phone app the last time the batteries ran out.
    For those of you with Android devices, I highly recommend:….
    There is a menu option to switch between RPN and whatever that other system is called…

    • I use both the HP 33s and a phone app. Both are set to RPN. I get confused when I use a "normal" calculator.

  • steve

    I still have my original HP-35 — $395 when new when the dollar was worth a lot and a huge sum for me in college. It has been through several battery changes, but I still use it every now and again. I only use rpn calculators on my phone … you get used to it (in about 15 minutes) and there's no going back.

  • Ross

    I have used the mathCalc app on my iPhone for years. It emulates an old HP reverse Polish notation calculator. I think it is similar to the 12C. I had a 41CX back in the day.