from Hacker News

Free42 – An HP-42S Calculator Simulator

by abiro on 5/11/23, 10:25 AM with 35 comments

• by userbinator on 5/12/23, 3:20 AM

  This IMHO very important information is buried near the bottom of the page:

  The HP-42S represents numbers with a 12-digit decimal mantissa, and an exponent from 10^−499 to 10^499; Free42 Decimal uses a 34-digit decimal mantissa, and an exponent from 10^−6143 to 10^6144; and Free42 Binary uses native binary floating-point, which on all currently supported platforms is IEEE-754 double precision, with a 53-bit binary mantissa which is roughly equivalent to 16 decimal digits, with an exponent from 10^−308 to 10^308.

  In other words, results will not be exactly the same as a real HP-42S. For a more authentic HP-42S experience, there's Emu42.

  Also, just about every dedicated calculator uses decimal floating point for several reasons, such as simpler circuitry in the ASIC and keeping the human intuition that 0.1 + 0.1 is actually 0.2.

• by banana_giraffe on 5/12/23, 2:11 AM

  For anyone that wants a physical version, SwissMicros makes a calculator based off of Free42: https://www.swissmicros.com/product/dm42

• by tigerlily on 5/12/23, 11:30 AM

  This app is my daily driver. It was hard to find in the App Store though when I searched for rpn calculators, it was a huge relief to find it.

  Little known perhaps but you can tap the display to bring up the main menu. From there you can optionally select a different skin. I use GDW-Modern-i5, a nice clean darkmode with orange highlights.

  Edit: actually you have to download new skins from a gallery webpage first via what I can only describe as a tiny embedded web browser you can bring up by clicking "Load..." in the bottom left corner. Truly this must be God's own calculator app.

• by idcrook on 5/12/23, 2:59 AM

  I had an HP 42S in college. was best calculator I have ever owned, and had used the programmable features in it.

  I have used Free42 on Macs and iPhones for years. love it.

  Plus42 improves upon it by expanding the display size, suitable for the aspect ratio and size of iPhone screens and Macs

• by dm319 on 5/12/23, 2:09 PM

  I've used the free42 (and newer plus42) app on my phone for nearly a decade now. In the UK, RPN calculators were pretty much not seen in the school place. We had Casios, Sharps, and those really into maths tended to get TI graphing calculators.

  The beauty of RPN is that you can get the data into the calculator before you figure out how you're going to calculate the thing you want to know. The roll and x<>y help you to manipulate the data, and once you get the hang of it, algebraic notation feels slow and unintuitive (back pedalling through notation to get brackets in place for example).

  You also get intermediate results to sense-check as you're going along.

  I recently got a DM42 from swissmicros, which is a real life calculator running free42. It is beautifully made, and it makes me happy that I have it. But my job isn't in one place, so I still probably use the phone app more.

• by crimsontech on 5/12/23, 2:36 AM

  There is also Plus42 by the same person which is what I use on my phone. https://thomasokken.com/plus42/

  I have a 42S and 15C, I tend to use Plus42 the most, then the 15C.

• by FullyFunctional on 5/12/23, 2:49 AM

  I have Free42 on my iPhone and while I don't use any of the advanced features, it has a level of polish that really makes it stand far from the crowd. Probably the most noticeable feature is the haptic feedback (enabled in the hidden menu under the logo). That feature and the full screen graphics goes a long way to making the calculator feel real.

• by joezydeco on 5/11/23, 7:41 PM

  I've had the iOS version of Free42 in my pocket for over a decade now. My real 42S is safe in a drawer. Highly recommended.

• by antod on 5/12/23, 2:37 AM

  The 42S was my calculator as a structural engineering student in the early 90s.

  I now regularly use the Android version of Free42 - I should try and find my old manuals though, so I could operate it as well as I used to.

• by nologic01 on 5/12/23, 7:58 AM

  This reminded me that after 30 years I need to change batteries on mine.

• by sytelus on 5/12/23, 2:07 AM

  Amazing! Now, if you only have this for HP-48SX :).

• by Bud on 5/12/23, 2:09 AM

  Am I the only one who think the 41CX totally outclasses the 42 series?