# Whatever happened to …

… RPN Calculators?

A couple of things came together that made me think about this.  First was a post by Deanna McLennan “What Does Equal Really Mean? Exploring the concept of equivalency in guided and playful explorations“.  My thought was that those kids would be really screwed if you gave them a calculator without an equal key.  Then, I was out shopping with my wife for things where my opinion and lack of patience really aren’t wanted.  So, I killed some time in the electronics section and wandered around the calculators.

I was actually kind of surprised that they are even still for sale.  Since most people have portable computers, tablets, or phones, a device to do a specific task seems like a waste of money.  But, there they were.  They ranged in price from \$5.99 to \$89.99.  And, they all had equal keys on them.  These algebraic calculators ranged from the simple four functions to some that looked like they would do some great scientific work.  Provided, of course, you know your algebra!  That’s not always easily said these days.

I remember the first student to ever have a calculator in high school.  It was today’s tablet sized and it was pure magic that he could do such great things with it.  It was magical.  But, once we got to really involved questions, he had to write down some of the intermediate calculations.  We didn’t feel terribly sorry for him because we had to write everything.  It also changed school policy where calculators were now banned from exams.

It wasn’t until university when I needed a calculator.  I most certainly lusted for one but my on-paper skills continued to be refined and lack of money was an even bigger consideration.  It wasn’t until stats class and our professor said that we needed a calculator.  If you’ve ever taken statistic, you know why.  She showed us a couple of models and really advised that we consider the Hewlett-Packard HP21.  It used RPN to solve logic.  Snicker.  Did she just say “Reverse Polish”?

Thanks, Wikimedia

I remember making an office appointment with her to talk about this since it was no small investment in those days.  She showed me how many fewer keystrokes it took to solve a problem than an algebraic calculator.  I was sold.

It was no easy learning curve.  You really had to know your mathematics because you didn’t solve problems left to right; you needed to know the order of operations and pushing and popping to and from a stack became common jargon.

That wonderful calculator followed me for years.  There wasn’t a problem that I couldn’t solve very quickly.  I think I always had more confidence in my answers because I was always showing in my mind the intermediary answers as I worked through a problem.  It wasn’t getting to the end, pressing = and then saying “that doesn’t look right”.

In my first years of teaching, some students were fascinated with how quickly I could solve problems.  As I suspect with most computer science teachers, it was the inspiration for many programs – write an RPN simulator, convert an algebraic expression to RPN and back again, counting the number of keystrokes and comparing efficiencies.

Sadly, there came a time when the batteries wouldn’t hold a charge.  Personal computers came with a calculator so having a device devoted to just doing calculations seems like overkill.  Plus, if you looked for the Advanced settings for most software, there was so much more that you could do.

These days, your phone or tablet comes with a calculator and a store devoted to hosting apps that give you so much.  I’ve upgraded to an HP67 on my phone

and have a Tausendstern on my iPad.

I don’t necessarily do a great deal of really involved calculations these days on a calculator but sometimes I just do some for the fun of it.

In preparing for this post, I did check the HP website and there are still a goodly collection of calculators, including RPN, there should you need one.

I guess RPN isn’t necessarily history.

• Do you still use a calculator or have you opted for the app on your device?  If so, which app?
• Have you ever used an RPN calculator?
• Computer science teachers – do you have students write programs to simulate RPN?

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## 3 thoughts on “Whatever happened to …”

1. Two of my CS students opted to write an RPN calculator this semester (given the choice to write almost anything).
Physical calculators are still useful because they have tactile buttons. You know what you pressed! The popular iPhone calculator is powerful but students make a lot of mistakes by tapping the wrong values or operations.

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2. zamanskym says:

Unfortunately, due to oversized influence of corporate influences on US Ed, calculators will be with us for a while. Basically, every kid taking AP Calc in the US has to use a TI graphing calculator, books use them as models etc so while there are better free programs out there for computers and phones, kids still have to fork over cash to big business.

All that said, I still have my trusty HP48 and still show it and talk about HP calculators – we have HP calculators and langauges like forth for postfix and contrast that with scheme/racket/lisp for prefix.

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3. I find the specialized graphing calculator to be ridiculous when we have much more versatile phones/computers/etc. which are already paid for and available. It’s not just corporate influence, though; it’s the “no collaboration allowed” evaluation approaches used. Can’t let kids use connected devices if you’re trying to test them, eh?

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