The R47: A new physical RPN calculator

11/11/2025 at 4:07:07 PM

There was a time when I would have salivated over this. But now I can run iPython on my phone, and have numpy, sympi, scipy, astropy and countless other packages. Physical keyboards are great for calculators - much better than virtual keyboards on phones. But the keyboard advantage seems to me most valuable for quick calculations, not elaborate things like this calculator offers. If I'm going to do matrix calculations, I want to be able to put the data into a file with a real, and familiar, editor. I want to be able to grab tables of data from the web. If I make a plot, I want to be able to save it to a PNG file. I want a high resolution color display. A phone running iPython/Python seems much better to me, especially since almost everyone who would want to do what this calculator does already has a smartphone. Also, I can ssh into my phone and interact with it using my desktop computer's keyboard and monitor, eliminating the phone keyboard limitations when a full sized computer is nearby.

by PopePompus

11/11/2025 at 8:11:32 PM

I don't really disagree with anything you've said, but I still feel a warm spot in my heart from projects like this. I still have (and use!) my HP48SX from my high school days, and it still works like it always has. There is something to be said for a device's limitations, and I mean that honestly. It's very powerful for what it is, but its processing limitations keeps me from overextending, which is something very easy to do with the pocket supercomputers we've all gotten used to carrying around over the previous decade. (And its keys are simply a delight to press compared to even the best glass touchscreen.)

by Baeocystin

11/11/2025 at 8:24:25 PM

Even with almost all of my work done on a computer, with Python, MATLAB, etc. available in a few keypresses, I still keep a calculator on hand. I haven't come across a desktop calculator (including direct 1:1 software recreations of classic calculators) that's quite as user-friendly and efficient as grabbing a scientific calculator off my desk and typing in there.

There are just some user interface advantages for me in having a physical calculator. The only thing stopping me from buying this is the price tag.

by 0xTJ

11/11/2025 at 5:53:56 PM

Same. Although I have a few physical calculators, I rarely use them, because although for a simple calculation they're faster, when I'm already at a computer/phone, using that is faster, and when I want to do anything involving programming an actual programming langugage is better.

by Elfener

11/11/2025 at 7:37:05 PM

Physical devices can be great where you have dust and water issues that can make a phone nearly impossible to use.

Of course, then a $5 calculator may serve you better ...

by bombcar

11/11/2025 at 10:12:20 PM

My HP41CV died after a few decades and a full repair didn’t seem feasible. The Swiss Micro seemed tempting but I honestly really wouldn’t use it.

by ghaff

11/11/2025 at 5:24:07 PM

True but a dedicated device has its own advantages (and disadvantages). Despite high availability I dislike spending too much time on my phone beside quick uses.

by grugagag

11/11/2025 at 5:38:07 PM

Yes, the "On/Off" button is instant and goes directly to the point/prompt.

by wslh

11/11/2025 at 10:15:30 PM

Any netbook it's far better than a smartphone for input.

by anthk

11/11/2025 at 5:44:40 PM

What IDE do you use? this functionality sounds great.

by ct0

11/11/2025 at 7:24:46 PM

I use Android phones, and there are at least two ways to get iPython going on an Android phone.

The first is Termux, which provides a gnu userspace atop the Android kernel. This app is pretty old, and well-tested. There is an active and helpful Termux community. But it has some downsides: 1) The version of Termux in the Google Play Store is not the preferred and maintained version, although the Play Store version does work. The preferred version is in F-Droid, but the future of F-Droid itself is uncertain in the light of recent Google policy decisions. 2) Termux does not have access to directories such as /proc, /sys etc, which prevents some gnu/Linux utilities from working and 3) The Termux filesystem layout is very non-standard, so unless a program has been packaged explicitly for Termux, installation will probably be messy. I was able to get most, but not all of the Python packages I use frequently, to run within Termux. I could not get astropy to work, for example. Termux has nice usability features like pinch-to-zoom to change the font size. Termux requests a wakelock, and if you grant the wakelock then the OS will not throttle the app when your phone is locked.

The other option is the relatively recently added "terminal" app. terminal runs a plain-vanilla Debian Linux OS within a VM. Its file system is laid out exactly as you would expect, so if you want to get iPython and lots of libraries, you can just run the Anaconda Python installation script, and it will run unmodified with no errors. Nice! You can also install other nice desktop-style apps like VeraCrypt. There are a few downsides: 1) The OS will throttle the app, and occasionally kill the app, when the app is not actively being used interactively. 2) I have found no way to change the tiny font. 3) It's a Google app, so it might disappear for no good reason, as so many Google products do.

Both of these options work especially nicely on a foldable phone, because then the tiny phone keyboard is much less of an issue. A foldable phone plus the terminal app really is a pocket Linux computer.

by PopePompus

11/11/2025 at 9:37:43 PM

I can't seem to find a Terminal app produced by Google LLC in Play store. Could you share the playstore link?

by scandals

11/11/2025 at 10:34:17 PM

It's actually not in the app store, and it may only be available on Pixel phones. You get the app not by downloading it from anywhere, you just enable "developer mode" in the system settings, and the app magically appears in your app menu (the full menu, not on any home screen by default). There is a subreddit dedicated to this app ( https://www.reddit.com/r/androidterminal/ ).

I've never used a Samsung phone, but I think their DeX environment might allow you to do the same things that the "terminal" app supplies.

If you can't get either of the above to work, give Termux a try. It's not full gnu/Linux, but it's pretty close.

by PopePompus

11/11/2025 at 10:07:16 PM

A physical calculator is a tool, so is your python interpreter, but they are different tools for different purposes.

Mathematica does everything your python interpreter does and more — but that doesn't mean python becomes useless because of that. It's good for certain things, while Mathematica is good for other things.

Similarly with calculators (especially HP calculators), which have become a bit of a lost art (an elegant weapon for a more civilized age). I use them all the time when doing any kind of engineering or hobby work. Good luck using your computer with python one-handed in a workshop next to a CNC.

One thing I do agree with is that plotting functions or working with larger matrices on calculators makes little sense.

by jwr

11/11/2025 at 10:16:26 PM

GNU Maxima it's the best of both grounds.

by anthk

11/12/2025 at 12:38:53 PM

Can I use it one-handed in my workshop? :-) There is no single perfect tool.

by jwr

11/12/2025 at 7:57:35 AM

Maxima isn't a GNU package, is it?

by volemo

11/12/2025 at 8:04:29 AM

It's forked from MacSyma and released under a GNU General Public License (GPL).

https://en.wikipedia.org/wiki/Maxima_(software)

Cayley (1975–1993), now Magma, predates it somewhat and has recently been used to crack post Quantum cryptography candidates.

https://dl.acm.org/doi/10.1145/1089355.1089359

https://en.wikipedia.org/wiki/Magma_(computer_algebra_system...

by defrost

11/12/2025 at 8:55:24 AM

It's not a GNU project though.

(Maybe ggp is thinking of the Matlab clone Octave, which is?)

by shawn_w

11/12/2025 at 1:06:11 AM

Running in WASM!

by ted_dunning

11/11/2025 at 5:24:45 PM

This sort of reminds me of the Numworks, except this feels a bit more artisan (and expensive).

In high school, my friends got onto the Numworks bandwagon, and we even used them on the SATs and AP tests (they were explicitly allowed). To be fair, this is before Numworks locked down their calculators and the alternative firmwares (Omega) died off, but maybe there are jailbreaks now and things are as they were before.

by kaladin-jasnah

11/11/2025 at 5:48:54 PM

> except this feels a bit more artisan

The difference (as far as I know) is that Numworks (and Casio, etc.) are mainly used by students, while SwissMicros (and HP) are used for very quick problem-solving on the job.

by Elfener

11/11/2025 at 9:40:46 PM

Also any older folks who grew up with HP calculators and prefer RPN over the newer calculators.

There was a time when RPN was waaay better than the TI and other competition, but in my mind that time is now past us. I can use both designs well and will take a TI-89 over a Swiss Micros (mind you I own several) almost any day as it is more straightforward. That's my opinion anyway. This improvement over the DM42 is pretty cool though.

Another Swiss Micros use is for people who work in a lab with gloves and can use a calculator better than a phone.

by 7thaccount

11/11/2025 at 4:59:53 PM

Cool. I used an HP48SX in college, and when it finally died about 20 years later, bought 2 HP48Gs so I'd have a Lifetime Supply. (1 is on my desk, 1 is still in the box.) But I confess that hardly ever use my real HP48G anymore, because I have the Droid48 Android app, and the 99% perfect calculator that's always at hand is better than the 100% perfect calculator that's on a shelf way over there, most of the time.

So I doubt I'll buy this one, even though I'm happy someone made it.

by dripton

11/7/2025 at 8:00:08 AM

This is a project to imagine what HP would have made today had they still been making calculators. It is unusual for a newly designed RPN calculator to be released, although there have been several re-releases of older HP models, such as the HP-15ce, HP-16c, and a series of calculators made by Swissmicros - DM-15L, DM-42, DM-32, but all based on designs dating back 30-50 years.

The R47 has been many years in the making and is a small open source project which has collaborated with the Swiss manufacturer of calculators, SwissMicros. It has a superset of functions over older HP models and many more too, including complex solve, default 34 digit decimal precision, 1000 digit integers, graphing, extensive complex support, etc and is substantially customisable.

I have no affiliation with the project, but excited that there is a new RPN machine commercially available.

[0] https://youtu.be/5A-pmjawJg8?si=11Ehf5SnzkZF79-e

by dm319

11/11/2025 at 5:09:31 PM

I don't think HP would be making something like this.

The original calculators, from the discrete HP9100A onwards, pushed tech to its limits.

The HP65 (1975) was a jaw-dropping masterpiece. When most calculators were four function, and scientific calculators were still exotic, a pocket-sized programmable calculator with a magnetic card reader was beyond the imagination of most engineers, never mind most users.

This is more of a nostalgic tribute act. It's nice it exists. But it's looking backwards, not forwards.

by TheOtherHobbes

11/11/2025 at 7:03:34 PM

I have an embarrassing question... math has always interested me but by luck and circumstance I have had a pretty successful career without needing anything beyond college Algebra. Can anyone recommend a curriculum that a busy adult may be able to follow in their spare time? I just want to fill in blanks and explore what is possible.

by crims0n

11/11/2025 at 7:29:11 PM

For me, I set out to write a flight simulator from scratch following a book [1]. I learned a lot of linear algebra that way. Such that when I later took Calculus III in college (it was linear algebra) I aced the class.

(Also, reinforced what I remembered from Trig, I finally fully grokked it. Except for trig identities, ha ha.)

The book was targeting DOS and C++. I wrote it in C for the Macintosh. (That required that I figured out what was going on.)

Go write one in JavaScript using an HTML5 canvas as your buffer. (I made a quick pass at doing something similar [2] — but do it on your own, don't follow my link below or look for the sources for Phosphor3D on GitHub.)

[1] https://archive.org/details/build-your-own-flight-sim-in-c-d...

[2] https://engineersneedart.com/Phosphor3DTest/

by JKCalhoun

11/12/2025 at 12:37:21 AM

Did you finish your flight simulator?

by glimshe

11/12/2025 at 12:57:10 AM

College algebra is just rehashed high school algebra.

Math is a broad subject. This is something LLMs are actually reasonably good at: ask them for textbook recommendations, and get into a dialogue about which sub-areas of math you're interested in and what level you're currently at, whether you want pure math (more theorem-proof focused) or applied math (more practice solving concrete problems, e.g. finding lots of derivatives and integrals). Toss in names of books that have been recommended and ask where they fit in to the LLM's other recommendations.

LLMs don't understand the math, but they're trained on a lot of discussions and recommendations for math books, and have a reasonably good sense of what level different books are at.

Download multiple recommendations in each area and try them all out. Seeing how different authors start out approaching largely the same material will help you conceptualize it better than just relying on a single approach. There's no universal "right" book to learn from. I wouldn't buy non-free textbooks without trying them out first.

Youtube has a lot of math lecture series, which can help if you're stuck on a particular point, but they're not the same as doing problem sets yourself.

by harshreality

11/12/2025 at 3:57:20 AM

LLMs DO understand the math. At least Claude does. Seems to be able to solve linear systems, invert matrices, and do a significant amount calculus, and handle some seriously advanced math problems. I haven't probed the outer limits, but, so far, Claude has handled all the math problems I've given it so far.

by rerdavies

11/13/2025 at 6:31:27 AM

Even if a deep thinking LLM like Opus can get some math questions right when that depends on identifying the type of problem and applying a learned procedure, it's not going to be able to evaluate the pedagogy of math books it's never encountered, or at most was fringe material in its training set.

I'm also referring to the faster models, not the slow and expensive deep thinking ones which I have little experience with. I don't see how reasoning would enable deep thinking models to meaningfully evaluate textbook pedagogy, either.

by harshreality

11/13/2025 at 3:02:57 PM

It seems pretty silly to make pronouncements about what LLMs are capable of doing if the sum total of your experience is casual use of the cheapest and least capable LLMs. (ChatGPT: measured IQ of about 70, vs. measured IQs of 120+ for more capable models, some of which are available for free).

They DO understand what they are doing. When I ask it to solve math problems, it goes through the several (many) steps involved (e.g. e.g. "apply the chain rule" while doing partial differentiation on a term in a Jacobian matrix). It gets pretty tedious when solving systems of linear equations, where it goes through each step of the Gauss-Jordan elimination while doing an LU decomposition, row by row. But one learns to ignore the blah-blah. Step by step, in absolutely ridiculous detail. The point: they absolutely 100% understand what they are doing, and understand it in minute detail.

It's clearly NOT regurgitating something that it has literally seen before, because the level of detail is beyond ridiculous for a human. It is applying generalized rules to specific concrete problems, and doing so with some level of strategic thinking.

Where did it learn those generalized principles, and how did it learn to do that? With absolute certainty, there are math textbooks among the materials they have been trained on. And they certainly learned it from SOMEWHERE. Probably math textbooks. How did they learn to generalize and think strategically? Well, that's the big mystery, isn't it? But they do.

The very best models achieve high scores on Math Olympiad problem sets (so competitive with some of the best minds on the planet). And Terrence Tau (greatest living mathematician) declares state-of-the-art models to be "better than most of my post-graduate students".

And what they can and cannot do is increasing by leaps and bounds on a weekly or monthly basis right now. It's hard to keep up. I frequently find that they can do things this week, that they could not do a week or a month ago. Startling, and quite utterly amazing.

Most of the time, I am using Claude Sonnet 4.5 as my coding agent, for which I pay $10/month. Measured IQ of 110, I think, with an IQ of 120 if you flip it into thinking mode. But only because there isn't enough undergraduate level mathematics in a standard IQ test. Claude Sonnet 4.5 is also available for free here: https://claude.ai/chats (during periods of heavy load, it may fall back to simpler models). I often use the free web interface instead of the Coding Agent interface for math problems, because it's easier to read mathematical equations in the browser version. version). And I generally use the free version of Claude instead of Google Search these days.

by rerdavies

11/14/2025 at 2:06:24 PM

You're arguing things I didn't argue. The top-level comment wasn't about how to do some math problem that Sonnet or even Opus is capable of; it was about math book recommendations, and I was specifically mentioning that even though the LLM won't understand the math pedagogy behind why one book might be better than another, it's trained on enough commentary that it will give good recommendations (or anti-recommendations) for any well-known textbooks.

My experience with people who have LLM subscriptions of any kind is that they use them all the time and would immediately ask an LLM that kind of question, rather than asking on a web forum that's not even dedicated to math. So I think it's a fair presumption that someone asking that question doesn't have access to the best commercial models.

On the largely irrelevant question of what math LLMs can do, although Opus may do better, Sonnet can follow procedures sometimes but not consistently. It has blind spots and can't scale procedures; beyond certain numbers or dimensions or problem complexity, it just guesses (wrong). And those limits are quite low. If you want 2 simple examples:

4294967297*1331

Invert this matrix: m=[1 0 5 0 3 7; 2 3 0 3 3 2; 1 0 1 1 0 1; 3 5 3 5 1 2; 2 4 3 2 1 5; 1 0 5 2 1 5]

LLMs follow procedures, but whimsically. Better LLMs will be less whimsical, but they still won't be fully competent unless they digest questions into more formal terms and then interface with an engine like Wolfram.

by harshreality

11/12/2025 at 12:47:54 PM

I wanted to brush up on my mostly forgotten high school math and found a free online course which used this ALEKS [1] tool. It was perfect for my situation.

It was some course on edx [2]. Can't find it right now, but you might find another course which uses it.

[1] https://www.aleks.com

[2] https://www.edx.org

by fainpul

11/11/2025 at 7:09:12 PM

I don't think that's embarassing.

I like solving math puzzles, and I'm often realizing that I'm missing something I've forgotten since middle school or high school - some formula that I know exists that would make a problem trivial. I'd like to re-learn that stuff, especially as my kiddo starts advancing in math classes.

by pavel_lishin

11/11/2025 at 7:07:58 PM

mathacademy.com is pretty awesome IMO. one hint: don't take notes/allow yourself to refer to notes during quizzes and reviews, the point is to be able to recall using just your brain, even if your progress is much slower that way, you'll learn a lot better.

by jerkstate

11/11/2025 at 7:29:04 PM

Many studies concur that the act of taking notes dramatically improves your ability to remember what you wrote, even if you never look at the notes again. You generally don't have time to transcribe a lecture like a stenographer would, so note taking requires you to understand the material enough to summarize it and describe it in your own words.

Don't rely on your notes come quiz time, if you can get away with it, but by all means do take them during the learning process. And in the real world, you're allowed to refer back to your notes as often as you want to.

by kstrauser

11/12/2025 at 6:52:42 AM

I've heard of adults going through Khan Academy's math curriculum for fun to refresh their math skills. It goes from K to 12 and up to 2nd or 3rd year university math, including calculus and such.

by fouc

11/11/2025 at 7:18:21 PM

I appreciate the quality of the engineering and design, and that the hardware is open to being tinkered with by means of firmware update. The price seems fair for what is offered, and the device looks like it would be very useful for anyone who doesn't have any computer at hand or readily available. Kudos to the project team!

But it's unlikely that I buy one because (1) I tend to be close to computers most of the time, (2) my favorite "HP calculator" is the HP9000/715 due to its sizeable HIL keyboard, its 21" CRT color screen, and its support for HP-UX, pun intended; and (3) most of the mathematics I need beyond paper, pen and blackboard can best be done in a Python Jupyter Notebook (statistics) or Mathematica (symbolic derivations).

by jll29

11/11/2025 at 5:53:01 PM

I think I will stick with a TI-89. No RPN, but that’s not necessarily a problem. More importantly, it has a CAS (Computer Algebra System). I wonder why CAS aren’t more common on such calculators. The technology exists since decades and it’s great. I know it’s not allowed in some school exams, but calculators already have exam modes.

by speedgoose

11/12/2025 at 8:43:03 AM

HP-28 series had CAS (first released in 1987), they were replaced by HP-48 series which also had CAS.

RPN was lovely because it was significantly faster to operate with. I remember showing up at math class having just received an HP-48G "because it's what the engineers use" and everyone else just got TI-89s because that's what the teacher had (TI gave teachers free TI-89s and did more marketing). The math teacher hosted an impromptu calculator speed contest and I beat out everyone else by a significant margin.

by fouc

11/11/2025 at 7:56:41 PM

Yeah I won't give a serious thought to anything that doesn't have full symbolic support. I gave my nephew-in-law my old TI-89 Titanium last year, he was entering 8th grade and I got it midway through 9th grade and it served me well all the way through my CE undergrad. Arithmetic, trig, statistics, basic calculus, differential equations, laplace transforms, vector calculus, it handled so much, and it was easy to use TI Basic to add new functionality/shortcuts... Prior to that I was happy with a cheap non-graphing scientific calculator (I think it was a Sharp EL-531WBBK Translucent Blue). It was fine for algebra, trig, geometry, and pre-calc science courses.

My dad has an HP-15C that I've always thought was cool but I never really liked to use it for anything. This new calculator is also really cool but I can't imagine ever owning one. I don't need to do much calculation anymore anyway so it's not like I need any calculator at all (hence giving away my old calc). I'm also usually at my PC, or a laptop, or I can ssh to my home system with my phone (if the phone's basic calc app is insufficient). For simple calculations I've most commonly used a Python repl since like 2007, but for anything more advanced these days I'd pull out one of the PC programs I was exposed to in the later parts of college (e.g. matlab or octave+symbolic and other packages, or maxima). But I also have used Python + libraries or Lisp + libraries, and would like to someday redo my Stats education with R. Hand calculators just seem really antiquated to me now.

by Jach

11/12/2025 at 12:01:31 AM

check out the HP Prime sometime. I got it for myself in a moment of retrocausal nostalgia and it's pretty awesome. I'm using 95% of my willpower not to get this linked product haha. Moving around a 3D surface with my finger just never gets old

by arthurcolle

11/11/2025 at 6:44:43 PM

Looks like it might be the same Sharp memory LCD screen that's on the Playdate? 400x240 monochrome LCD display, roughly 2.6-2.7" diagonally?

by rickz0rz

11/11/2025 at 7:36:53 PM

I think it's likely - from what I can tell only Sharp makes these displays. I've been looking for displays like these (no backlight, fast refresh) for a project and all I could find was the Adafruit breakout of that one.

by a3c9

11/11/2025 at 4:01:45 PM

Ooh, I'm going to have to download the emulator tonight and try this out. The swiss micro and 47calc sites both say "display with 4 stack levels", but I can't figure out if that is also the size of the logical stack.

The shift key on my HP28C died last year. I never used the advanced features (eg the entire left-hand keypad), but loved its effectively infinite stack, and haven't been able to go back to an HP42, HP35s or the like since.

I'm now using Plus42 on my phone with the big stack option, but would love to have a physical calculator again.

by pavon

11/12/2025 at 5:32:42 PM

The C47/R47 appears to use the 4-level XYZT stack design by default, but it has an option to use an 8-level stack (XYZTABCD). I really like the unlimited stack option that can be enabled in Free42, but 8 levels might be enough to keep from feeling cramped in practice.

by jasone

11/11/2025 at 6:09:43 PM

“Display with 4 stack levels” would accurately describe the hp 48 series, which had a screen that could show the top 4 things on the stack, but the stack itself had much larger capacity (maybe limited by memory? I can’t remember).

by hamburglar

11/11/2025 at 7:58:40 PM

I'd love to see a non-programmable version. If I recall it would be something like the HP 10C. It's because I just want the RPN part along with math functions.

A good example: Taking your FCC ham license exam does not permit use of your phone or a programmable calculator. They would have allowed me to use it.

I had practiced for the exams with my old HP 11C. It was jarring to have to switch to a TI calculator during the test.

by idatum

11/11/2025 at 9:44:35 PM

Swiss Micros makes several reproductions of old HP calculators such as the 11c, 12c, 15c ...etc. I know the 15c has keystroke macros, but not sure about the 12c.

Edit: it looks like you're right and they're all programmable. My mistake.

by 7thaccount

11/11/2025 at 6:49:02 PM

> Processor ultra-low-power ARM® Cortex-M33®, at max. 160 MHz

> Battery type 1 × CR2032 3V lithium coin cell

Very nice. Impressive.

by creer

11/11/2025 at 6:02:21 PM

I'm sort of surprised by SwissMicros focus on the 42. I have a 42S and a 48GX and the 48GX is IMO far superior in almost every way. My only complaint is that the UI can be sluggish in places, but with a modern CPU this would completely go away, and it does on the 49, which I also have, but unfortunately its screen died and the keyboard stinks. The 48GX was the last model I have where they actually built it with some quality.

by cameldrv

11/11/2025 at 6:13:18 PM

Still got my 48GX, 49G, 19BII and 28S. The 49G is the only that is unusable (rubber buttons? Really?).

49G aside, they all are good enough for use although probably no longer usable in some of their intended uses (re: any formal tests that would allow them?).

by cmxch

11/11/2025 at 3:54:44 PM

I still have my HP 48G and love it. I don't use it much and take the batteries out so they don't corrode in the case.

Every time I use for more than a couple of calculations I think how much I prefer a RPN calculator.

by fm2606

11/11/2025 at 4:28:57 PM

The DB48X project created a HP48G/HP50G style firmware for SwissMicros calculators.

https://github.com/c3d/db48x

by ch_123

11/11/2025 at 5:08:50 PM

The db48x/db50x project seems to be more promising than C47/R47; although, I wish Swissmicros could produce a db50x version with the right layout (no stickies)

by natas

11/11/2025 at 11:07:04 PM

An extra row of keys to match the HP48 would be useful too.

by ch_123

11/11/2025 at 6:07:33 PM

Mine is unfortunately now dead - the display has gone dark even though the device is functional. At some point I'll have to look into a repair or replace with something from SwissMicro.

by abawany

11/12/2025 at 8:49:54 AM

I used an HP-48G heavily in school.

Just now I tried out the RPN calculator apps on the phone and I've realized that the enter key to the left above the number menu forces me to use two hands if I want to operate the calculator fast.

I think it makes more sense to stick the enter button at the bottom right near the other arithmetic operations, then I can at least operate the calculator reasonably quickly with just one hand for arithmetic.

by fouc

11/11/2025 at 5:51:23 PM

I still have my HP-42S 30 years after I finished engineering in university. Just an awesome calculator that still has that awesome tactile button feel.

by outside1234

11/11/2025 at 5:54:23 PM

Is this the DM42n hardware with the R47 firmware preloaded? It looks identical, except for the colors of some of the keys, and I wouldn't think they'd have a separate hardware pipeline for it. I could be wrong, though! If someone were to obsess over their gear and tweak it until it was just so, this would be the company to do it.

by kstrauser

11/11/2025 at 9:43:47 PM

Yes, it's the DM42n hardware underneath. The keyboard and overlay are different and the firmware is written from scratch using the WP 34S mathematics code. This has a lot more functionality than the DM42n does.

by pauli5

11/11/2025 at 7:53:10 PM

Release a souped-up all-metal HP 200LX and I'm gonna be a customer (x86 with AAA batteries, no ARM workaround).

by spankibalt

11/11/2025 at 10:37:21 PM

My college girlfriend had an HP RPN calculator of some kind (42s?) that was non-graphing. She loved the calculator and never wanted the bulkier 48sx graphing one her Dad bought her, which is how I ended up with it. I kept it after the breakup and she got a Sony boombox. The HP still works 31 years later.

by lisbbb

11/11/2025 at 6:19:18 PM

Maybe it's a generational thing -- I haven't had to use a standalone calculator in my professional life -- but what's the benefit of using RPN as opposed to the more common infix notation?

Beyond that... do RPN calculators like these usually include the option to use infix notation?

by _verandaguy

11/11/2025 at 6:31:55 PM

It eliminates the need for parentheses and operator precedence, which is honestly nearly half of the character count of my usual infix math. You can just keep performing new calculations and then later on decide how you want to combine them. It's pretty great.

by xyzzy_plugh

11/11/2025 at 6:32:59 PM

The iPhone calculator, for example, only recently added parenthesis. However, with prefix notation you have to plan out your open parenthesis, and if you forgot one you have to back up. With postfix, the parenthesis are implicit. Which is faster? “2 2 + 2 x” or “2 + 2 = x 2 =“ for 2(2+2)

by TheJoeMan

11/11/2025 at 6:37:41 PM

On a basic four-function calculator, you can do "2 + 2 x 2 =" to get 8 without the extra = in the middle. RPN really shines when you use the stack for real. "(2 + 3) x (4 + 5)" is "2 3 + 4 5 + x" in RPN, but on a four-function this requires the stateful memory buttons and gets out of control fast. You may need to spill out to pen-and-paper with a four-function calculator, but you never need that with RPN. I'm less certain that the comparison works out in RPN's favor if you have a calculator with parentheses--where are you getting the complex expression that you're entering? If it's on paper, then it's already in infix notation and you had to mentally convert it to RPN inside-out. Entering the infix notation may be more keystrokes but likely less mental effort because it's more of a direct transcription. I taught a sibling how to use an HP-12C and I don't think they're ever gaining that time back in efficiency.

by electroly

11/11/2025 at 7:04:50 PM

Way back around ‘84 in the military I was doing the artillery survey calculations for the Lance (potentially nuclear) missile. We had to store first the program into the volatile hp memory, run check calculations before doing the real calculations. I always found the calculations very efficient - they had to be as they had to be done within certain time limits (and independently checked). It was a strange feeling thinking about doing the calculations under high pressure and what the stakes were if you would get the coordinates or directions wrong in case it would be used.

by heisenbit

11/12/2025 at 12:55:22 PM

Beyond the fast entry (no parentheses), I like RPN because I find it a more intuitive way of working with numbers.

I do not need to think about my operation before I start inputting numbers. I can type in the numbers I'll need, and while seeing them I run operations on them.

by benhurmarcel

11/11/2025 at 7:35:23 PM

I have an HP50G that lets you switch to infix notation, but for most operations RPN is faster due to fewer keystrokes.

Like many others here, I rarely use my calculator any more. My phone is just so much more powerful with a lisp REPL and python.

This is cool technology, though.

by stackghost

11/11/2025 at 8:19:01 PM

The only calculator I still use is a business one (and these guys sell those too it seems!). It’s super handy for figuring out interest rate stuff, growth rate stuff etc. for anything simpler or more complex, it’s just easier to use a phone or more checkable to use a laptop.

by clickety_clack

11/11/2025 at 7:12:04 PM

Super cool! But I so rarely reach for the physical calculators I already have these days. Any recommendations on RPN calculators for Windows or Android? The one I've got on my phone right now has some little quirks that bug me.

by mintplant

11/14/2025 at 10:09:44 AM

RealCalc (Android) is the one I use all the time. Emu48 (Android, Windows) emulates HP48GX hardware and runs an actual HP48GX ROM image. NumWorks (Android, Windows, web) emulates a NumWorks graphing calculator - has some nice features, but not RPN.

by boisterousness

11/11/2025 at 10:20:49 PM

I use one called 48sx, however, I've only ever used +-*/. Clicky physical buttons are much better of course. An accountant I worked with years ago had one with a printer, which meant she had a paper record and could verify that the entries were correct.

by bolangi

11/11/2025 at 9:18:38 PM

Which one do you have on your phone? Plus42 for Android has been mentioned. I like Droid 48 (also Android).

by manithree

11/12/2025 at 4:42:21 AM

Hiper is pretty good (I paid for it, even) but the the lack of undo really winds me up.

  1
  2
  + (->3)
  9
  + (->12)...no wait I meant 99
  ...uhhh what did I just do...9?
  9
  -

by georgefrowny

11/11/2025 at 5:07:05 PM

Honest question but who would need this these days? Would this calculator still be useful for professors/mathematicians/etc or is this more for HP calculator enthusiasts?

by _fat_santa

11/11/2025 at 5:14:46 PM

I work in industry automation and use for every day calculation mostly my HP 35s, even I also have a HP 50g under my desk and more than a PC on my desk.

It's just for me the most easy way to calculate things with current and power for everyday use.

And .. even the basic Windows calc app is so slow to start, I already finished until the app started.

by _trampeltier

11/11/2025 at 5:27:30 PM

I have a 35s as well; I was made fun of for using one (you know you're sitting at a calculator that is 1000s of time more powerful right?). I still use it.

by aidenn0

11/11/2025 at 5:31:09 PM

A F1 car has more Hp than any tractor and is still useless for any farmer.

by _trampeltier

11/11/2025 at 6:43:28 PM

Just as a fun fact, some of the largest tractors made these days actually rival F1 cars in horsepower output. John Deere 9RX goes up to 913 HP for example.

by auxym

11/11/2025 at 5:37:17 PM

My HP 35s sits between the 2 halves of my split keyboard. I use it multiple times per day. It's just faster for quick calculations as the UI is very well done and it turns on instantly.

by bradfa

11/11/2025 at 7:21:03 PM

I bought a 35s and found the ergonomics not as good as my old, dead 11C. So I bought an antique 15C on eBay, and it sits right by my keyboard all day.

I'll use the built in calc in macOS Spotlight for many things, but plenty of times each day I use the HP. Example: yesterday I calculated an angle in degrees by reading off approximate x, y coordinates from a graph on my screen. Swapping windows to a calculator app, repositioning them to see both at the same time, just too fiddly, and clicking the calc app moves the cursor so I have to remember the numbers as I switch context.. The physical HP in front of me leaves my screen undisturbed. Easy.

by hughw

11/11/2025 at 7:46:14 PM

It's probably not a necessity - I'm sure I could adapt to just using my smartphone if I put the time into learning some of the math apps. I still use my ti-89 for everyday calculations. It's a handy device; more portable than a laptop, and better UI than a smartphone. I don't deny myself from using a tool I like.

by DanTheManPR

11/11/2025 at 7:22:35 PM

Good question. I still use an HP42S these days, but it's an app on my phone or desktop not a separate device. Replacing batteries was a big pain on the original.

by antod

11/11/2025 at 5:54:07 PM

I use an HP-16 (the SwissMicros version, my originals are in boxes) and a 35s pretty much every day (these days, I'm writing firmware).

by kabdib

11/11/2025 at 3:41:11 PM

I really want one, but 250 credits is quite a bit too much. Even at 100 credits I'd be questioning my sanity, to be honest.

by globular-toast

11/11/2025 at 3:53:39 PM

Its ~300 USD. I wonder who the target audience is.

by NewsaHackO

11/11/2025 at 4:28:01 PM

There is a community of folks who are really into this firmware, and a lot of those people buy SwissMicros other models of calculators, (e.g. DM42 or DM32) and put keyboard stickers on it. This allows them to buy the model with the correct key legends up front.

The low volume and the relatively high build quality involved pushes the prices up.

by ch_123

11/11/2025 at 5:36:39 PM

I can see that. The build quality and screen both seem to be very high end.

by NewsaHackO

11/11/2025 at 6:14:03 PM

I have a few Swiss Micros, but rarely use them. Beautiful devices though. Built to last forever.

by 7thaccount

11/11/2025 at 7:35:17 PM

Terrible keyboards though. At least compared to my beloved 48s and 28.

How Id love for SM to do a straight 48G with more memory and a good keyboard. (But keys are hard to do)

by shtzvhdx

11/12/2025 at 9:56:16 AM

I believe they made improvements to their keyboards in recent years. My DM42n has a decent keyboard. Main criticism compared to my HP48G is that the keys are on the small side.

by ch_123

11/11/2025 at 9:48:31 PM

My DM42 feels great. I haven't touched a 48g in ages though, so can't compare.

by 7thaccount

11/11/2025 at 10:43:14 PM

[dead]

by veegee

11/7/2025 at 8:43:15 AM

Already Out of Stock. I want one :-(

by macmac

11/7/2025 at 9:00:12 AM

The release day is meant to be today, the out-of-stock just means they haven't opened yet.

They've asked people to purchase a voucher on the C47/R47 site for an early-bird discount which will send some money towards the developers. This voucher can then be used to get the calculator once SwissMicros take bookings. The link is at the bottom of the Swissmicros page.

by dm319

11/11/2025 at 4:20:29 PM

I still miss my 15C.

by drob518

11/11/2025 at 5:06:13 PM

I still have mine from 1987. You can still buy the HP-15C Collector's Edition new, but it isn't as good as the originals with their perfect keyboards and the silicon on sapphire technology that gave them their incredible battery life. The SwissMicros DM-15L is also a worthwhile substitute.

by fmajid

11/11/2025 at 5:26:24 PM

> The SwissMicros DM-15L is also a worthwhile substitute.

I got my DM16L two weeks ago and I love it to bits!

They even upgraded it to USB-C (even though the product description still says Mini USB), which was a pleasant surprise. I only just got into RPN calculators (and programmable calculators in the first place) a month ago, loving it so far.

by Hackbraten

11/11/2025 at 6:14:51 PM

I got the HP15C Collector's Edition, because I always lusted after those HP calcs, and never could afford one. People in this thread asking: why? Well, many of the calculators on screen are simply worse, or copies of decent calculators but you have to press every button with the freaking mouse. A dedicated calculator feels nicer. Copy&paste is nice with an on-screen calc, I admit.

I do have a few other calculators as well, so I'm definitely biased.

by tgv

11/12/2025 at 12:49:14 AM

Yea, I’ve felt the new 15Cs and they just aren’t the same. Shame. I might have to give SwissMicros a try.

by drob518

11/11/2025 at 4:53:49 PM

There's a really good emulator for the iPhone! Back when I bought it, it came from HP themselves, but a few years ago they sold it to another company which actually maintains it. They just released a major new version a few weeks ago.

by mprovost

11/11/2025 at 7:25:53 PM

Yes, the new version is really nice now in portrait mode. Nice app. Now if only we could have tactile buttons...

by hughw

11/11/2025 at 8:54:35 PM

I have that and do like it even though it lacks that HP tactile feel.

by sizzzzlerz

11/11/2025 at 6:46:01 PM

Am I the only one who dislikes the CR2032 that all the RPN calculators need?

by GloriousKoji

11/11/2025 at 7:25:13 PM

No, although my old one (HP42S) used 3 of the smaller stubbier batteries.

by antod

11/11/2025 at 8:51:54 PM

I had a 48C that fed on those batteries. They lasted forever. I had to retire mine when the battery door broke and the batteries wouldn’t stay in. It was a great calculator from HP’s heyday.

by sizzzzlerz

11/11/2025 at 7:32:05 PM

How come? I admit I've never given it any thought. What do you dislike about them?

by kstrauser

11/12/2025 at 1:25:04 AM

Calculators are large enough that it should be possible to fit AAA or AA sized batteries, even possibly a 18650. They're lower power enough that a CR3202 lasts a long enough time but it always ends up dying at the most inconvenient time and they're really the only device I have that needs CR3202.

by GloriousKoji

11/12/2025 at 1:38:37 AM

You'd need two AAs or AAAs for a CR2032's voltage. While it would last a lot longer, it's also a lot more volume. Also, the diameter is going to be a problem for many calculators; e.g., the R47 being discussed here is 12mm thick, a AA has a 14.5mm diameter and a AA has a 10.5mm diameter.

by dragonwriter

11/12/2025 at 1:51:42 AM

Huh, interesting points. I wouldn’t have thought of that because I ended up with a passel of widgets using those cells, including car key fobs, Apple AirTags, and a number of IoT sensors around the house. I own exactly a single flashlight that uses an 18650. Go figure!

by kstrauser