The HP15C returns as an iPhone app

Editor’s note: Ken Coffman and Sanjay Maniktala have both written excellent blogs and articles for me in the past. On August 26, 2016 they both will be presenting a Workshop: Magnetics in Power Conversion. Maniktala will be speaking about Magnetics design and Coffman will be giving a brief overview of FPGAs for power engineers for which he has creatively titled: An Overview of FPGAs for Power Engineers. I recommend you attend this for some very good technical insights and added knowledge by these two excellent engineers.

While sitting in a meeting, I snooped at what my colleague was doing on his iPhone. I expected a Taylor Swift video or Pokémon adventure, but instead experienced a mind-wrenching experience. He was noodling away on his HP15C app. It’s probably impossible for younger people to appreciate what these HP calculators meant to people of my generation. Many of my friends loved the clunky HP42, but I loved the sleek HP15C and its brother the HP16C which was an Intel 8088 CPU in calculator form. I even still have the receipt from February 26, 1982 for $110 plus $7.15 sales tax. These calculators dragged my tired butt through engineering school and this was when, if you wanted to be an engineer, the classes were less user friendly and a hundred bucks was a lot of hard-earned money, not two burgers and a couple of frothy microbrews at a trendy restaurant.

We can still buy reverse-Polish calculators, but these HP number-crunchers were the ones that corrupted our pedantic minds forever. The beauty of the ENTER key, oh, it fills my shriveled heart with joy even to this day, but that’s not my favorite key. I love the CHS key. This key (or +/-) is common today, but not ubiquitous. Without CHS, you can do the same thing by entering the – sign before typing an exponent, but what sense does it make to have a display that briefly shows –zero? What a travesty. I prefer to load the exponent, then change its sign—instantly changing the number being exponentiated. If exponentiated is not a word, it should be.

I am an old-timer, so the shock of seeing something I love in physical form, virtualized, was an out-of-body experience. The folks at HP took the time and made the effort to create an HP15C calculator as an iPhone app. Of course, I couldn’t hand over my $14.95 fast enough—the efunds were transferred at nearly light speed. I see that the app has been around for a while, but I didn’t know. Clearly I don’t spend enough time goofing off on the Internet.

I wonder if my current employer would support an effort to create a CDP1802 CPU app. After all, to this day, it’s the only CPU you can have SEX with (SEt indirect register X). That has to be worth something.

What are your memories about the historic HP calculators? What did they mean to your engineering career?

Editor's comment: Also see Dennis Feucht's blog The Calculator: An Important Engineering Tool

4 comments on “The HP15C returns as an iPhone app

  1. TomC123123
    July 20, 2016


    Perhaps I 'have a few years' on you.  Early college was still slide rules.  By 3rd year, I spent most of my disposable income on an HP65.  Was laughed at by the profs, until it 'outran' the IBM1130 mainframe in a numerical methods course.  Great learning experience; still have it – just need to refurbish the card reader and battery pack.



  2. Koda23
    July 20, 2016

    I used an HP41CV in engineering school in the 1980's and still have it. It had the capability to print text on the screen and run short programs or sequences of calculations.

    After writing a short program, you could also assign it to a function key. A couple of the routines I stored and used a lot included calculations in dB, parallel combination of resistor values, impedance, etc.

  3. Victor Lorenzo
    July 20, 2016

    My first electronic calculator was only able to add/substract and multiply/divide. It was extremely basic but helped me a lot combined with my book of trigonometric function tables. The second one I had was a Casio fx-82 scientific calculator.

    One of our classmates was really skilled with the slide rule, it was hard for us to beat him with our electronic calculators, thought we used to obtain better error margins.

  4. Andy_I
    July 21, 2016

    My first calculator was an HP-35, when they were new.  I loved it.  Some of the buttons started getting flaky after years of hard use.

    To be followed by an HP-29C some years later.

    Then finally an HP-15C.  It still sits on my desk in front of me, and it gets used at least a few times daily.  I can't remember how long I have had it (can it really be 30 years?).  I don't think I have even replaced the batteries.  It just keeps doing what it's supposed to do.  I would not want to be without it.

    RPN rules!

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