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.
as posted below:
For anyone that wants a physical version, SwissMicros makes a calculator based off of Free42: https://www.swissmicros.com/product/dm42
That website mentions that they use decimal floating point. Since free42 is licensed under gpl3, they have released the source.
https://github.com/swissmicros/DM42PGM/tree/master/lib
https://github.com/swissmicros/free42/tree/master/inteldecim...
They use Intel's library for decimal floating point: https://software.intel.com/en-us/articles/intel-decimal-floa...
It's still not the real HP-42S with its quirks, but it's nice to have decimal floating point operations.
Weird obscure fact: The printer head for HP calculator printer was still available as new parts as late as 2019, coz it was used in variety of devices, I bought cheap non-working one and just replaced the head
My understanding is that "decimal", in the context of programming, is a less-precise term to mean floating-point (i.e. encompassing IEEE 754 floats, double- vs single-precision, etc), because they're all binary numbers if you dig deep enough, right?
But apparently I am incorrect/underinformed about this.
What is "decimal", then?
HP was also working to rationalize its product line at the time. The 41 was introduced as the high-end offering, but a few years later, they also introduced the 28C/S. These were intended as next-generation offerings. The 28 was arguably higher end than the 41, but it wasn't expandable and had a more cumbersome UI. For a few years, this left HP with two disjoint high end offerings.
To address this, HP slotted the 48SX in as a partial replacement for both the 41 and the 28. (Hence the name). The 48 improved on the 28 a bit, switched back to a traditional handheld calculator form factor, and brought in the expansion and bidirectional I/O from the 41. But it still had the more cumbersome UI of the 28.
The 42 was slotted below the 48 as a more direct replacement of the 41. A very similar UI to the 41 but built on the newer technology. A few years after all of this, the entire business essentially shut down. (See my earlier point on the emergence of personal computing, and particularly laptops. The calculator niche narrowed down to essentially the vanishing point, outside of education.)
Where this left the 42 is as the last and best of HP's traditional calculators. It's prized because of both the capabilities, and the lack of expansion doesn't matter that much. There are better options for that.
This is a long answer, I know, but the short story is that as a practical tool, the 42 is probably the better choice these days. (Although if you need something like an HP-IL barcode scanner or something, you need a 41.)
I don’t have a HUGE use for it, but it’s really well done, feels really sturdy and somewhat premium. It was amusing to learn (and re-learn on rare use) more advanced features and programming it.
Sure, one can do that with emulator but physicality adds to the fun.
I wish someone made modern keyboards with Amiga, Atari, Alto, Symbolics, Sun, or DEC LK layouts for use with emulated platforms.
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.
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
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.
I have a 42S and 15C, I tend to use Plus42 the most, then the 15C.
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.
Outside of that, as a calculator, the 42s is a better, more capable device.
Make no mistake, the 41 series was very cool. How many other calculators had floppy drives, plus whatever else you could wire into the 41.
But the 42s is just flat out a better calculator.
I have Free42 on my iPhone, but I typically reach for iHP48 over the 42. Just more comfortable with it.
