I had an HP-34C calculator in high school and college. Built like a tank. I loved that thing.
Another fond memory of HP: the HP Deskjet 1600CM. It was an inkjet printer with real PostScript. I had one in my lab twenty years ago. I wouldn’t be surprised to learn it is out there somewhere, still printing.
Steve Jobs never wanted to be in the printer business. He developed and built Laser Writers because he couldn’t convince even one company to build a desktop printer that could handle Mac’s very advanced Post Script technology that enabled super advanced typography, as well as PDF. At the time laser printers were very large sized and for high end professional printing. Canon was the leading player in the professional and desktop market, and my guess is it’s probably why Laser Writer stuff looked like Canon cartridges.
Somewhere in my collection of old devices is an HP 45 that I bought when it came out while I was a grad student at Stanford. Being down the street from HP’s headquarters, Stanford was a hotbed of enthusiasm for the HP 35 and then the 45.
My wife swore (and still swears) by the HP calculator (can’t remember the model) she got in college, used through grad school, and a career in a lab, and still uses in retirement.
I fell in love with RPN in high school when a friend of a friend visited and showed off his HP 35. Led me to start using RPN for normal math stuff on paper, much to the perturbation of a teacher or two. In college, a classmate had a 45, but when the 65 came out and he wanted one so badly that he hurled the 45 several times into a cement wall to break it so he’d be able to con his parents into contributing to the newer one. It refused to break. I didn’t get my first until the ‘affordable’ 25 came out, and my parents had a fit at the expense ($200, ~$1200 today); hard to explain to normal people why it was so important.
The HP manuals were also excellent. Spend a couple of hours going through one, and you knew not only every feature, but how they interacted and when to choose one option over another.
One of the old HP’s nice traits was that they were fairly generous about open source. Many of the older printers have open source drivers (possibly not as full featured as the commercial versions), and much or most of the calculator source is also open, so there are many emulators available–free, paid, and in dedicated hardware.
I’m partial to the RLM versions, first on Palm, and now on iOS. They’ve added quite a lot of nice extensions to the originals, including financial features, constants, conversions, and more. All of which are completely out of the way if you don’t need them. They have several calculator versions; I don’t remember what I had on the Palms, but I’ve had the RLM-11cx version since I got an ipod touch 2 lo those many years ago. No data collected, $10 for lifetime purchase.
For those who like the 41cx, there’s Antonio Lagana’s i41cx ($10) and i41cx+ ($25). The + version includes a Computer Algebra System (open source REDUCE) with graphics.
Hardware emulators–I don’t have one, but I’m tempted:
I’m still using my HP 15C, which I got as a Christmas gift in the early 1980s. It got me through graduate school, and has priviledged place on my desk, in it’s original padded case, complete with it’s tiny defect on the face where I once accidentally let a single drop of acid land during a chemistry lab.
It still works after all these years, and it remains my favorite calculator ever. I have an emulator on my phone, but still prefer the look and feel of the original hardware, and as others have commented the documentation was excellent.
It’s sad to me that the fine calculators of the past have been replaced by the current TIs which my kids were required to use. They really compare poorly to even my 15C, let alone something like the 48X.
Sure, my phone can do more and better now, but I’ll never prefer it to something with real keys that have such pleasing tactile feedback.
Ah, nostalgia. 
Kevin
I can vouch for the i41CX+ - it’s well worth the money. The i41CX+ is my go-to if I don’t have my 16C available or I need a function that’s not on the 16C. It;s a fine work and I haven’t even scratched the surface on what it can do.
When the HP35 came out I was blown away by its utility, beauty and simplicity but couldn’t afford its $400 price. Instead I bought a much cheaper TI calculator which used algebraic entry and, while fast and programmable, completely lacked the elegance of the 35, which I got to play with since a few of my coworkers in our lab had one.
When the price came down to $200 I bought a 35 and loved RPN. There was a language called Forth which used RPN and it was freely available for the Apple IIe, which I used to run my experiments (using Forth) with home made cards which plugged into the Apple bus (this was well before the Mac). I eventually rewrote the code in 6502 assembler for a tenfold speed increase. Interestingly, the Forth system had an assembler which required that code be written in postfix syntax, which took some getting used to.
There are a number of excellent HP calculator emulators, using original ROM code, on the iOS App Store. I have the one for the HP41C and the HP48 (free and a great app).
I found it interesting that RPN, which seems so natural to me, is not to everyone’s taste. For example, the author of the PCalc manual, an extremely smart fellow who contributes to this forum, finds it “a conceptually difficult mode of entry to master”. Tastes differ, I guess.
It is too bad that HP, which made so many innovative test instruments and calculators , degenerated into the maker of PC clones and currently substandard printers. What a tragedy for a once great company. (HP also did some cutting edge research in things like atomic clocks using trapped ions, similar to my research. A successor to this clock, built by my first grad student currently at JPL, is now in earth orbit doing interesting research.)
I still daily use my trusty old HP-15C (its nameplate has fallen off) from 1982. I have it right next to my main Mac in the lab. At my office I also still use my programmable HP-42S and I have another HP-42S at home on my desk.
When I was in grad school it seemed every physicist loved RPN and everybody had an HP as a calculator. Before that time my dad went straight from slide rule (I inherited about 5 of those from him – one even in ivory [is that still legal to own these days?]) to one of those original HP calculators with the red number display on black background (perhaps an HP-35?).
As a postdoc and then later on my first tenured appointment, I started seeing more and more graphing calculators, often TI, pop up among younger people. These days I rarely see an HP, but then again, I rarely see others use calculators at all. I guess most probably use their phones. There’s an excellent free emulator for the HP-42S that I use on my iPhone all the time. I’d love a 15C emulator too, but it seems those are all quite expensive considering it’d be just for fun.
The HP35 did use red LEDs for display. These were power hungry and limited the battery life (like those original LED watches which required a button push to read the display).
HP eventually went to LCDs. I don’t remember when that happened.
I was one of those who never could get the hang of RPN. My loss, I know…
No loss, algebraic entry works very well. I love programming on the Mac and never got the hang of object oriented programming. Using Swift with Metal on my recent apps was like pulling teeth (and thank God for Stack Overflow)
On my Mac I use Spotlight a lot as a quick calculator (since it’s only cmd-space away from whatever I’m doing) and so often I wish it could do RPN calculations. Every time I have to insert a parenthesis and then go back to the very beginning of my statement to add the opening parenthesis I sigh thinking back to RPN. 
On my M1 mini Mac, I nourish my craving for an RPN calculator with the GO-29 app
.
Not quite as quick to access, but Spotlight > Calculator.app > Command-R toggles RPN Mode.
“I’d love a 15C emulator too, but it seems those are all quite expensive considering it’d be just for fun.”
Try RLM-15cx. 30 day demo for the full thing, then a lifetime price of $10. I think that’s what I paid in 2008 for the 11cx version, and it’s been frequently updated including lots of new features, many useful, ever since. I’m considering getting the 15cx as well, partly because in the old days I wished I could have one for the matrix operations (bought the 11c several months before the 15c came out, sigh), but also to throw some extra money to an excellent developer.
https://www.rlmtools.com/RLM-15CX/index.html
I wish my real ones still worked though. The 25 died of no battery replacements available (I should look again, maybe third parties have stepped in) and the 11c started displaying nonsense. I might be able to get a friend to try and fix it for me eventually but I’m not holding my breath.
I’ve always been befuddled my object oriented stuff too. I can see some uses, but it seems like it became fashionable to shoehorn everything into that structure whether it made sense or not. Whereas it’s obvious to the most casual observer that functional* programming and recursion are the right and proper way to do everything. So long live APL, Lisp, and Logo. And I guess Python, since with a bit of care it can be used functionally and all that object stuff ignored.
Off topic, but I loved APL. In the late 60s I was a physics grad student at an IBM facility associated with my University and we had access, via Selectric 2741 terminals, to the computer (a 360/50) where APL was developed, I believe. Doing a )PORTS command yielded KEI for Kenneth E. Iverson, the inventor of APL based upon his book, A Programming Language, which described a very terse hardware description language with extensive array manipulation capabilities.
One can get a free version of APL for the Mac from the company Dyalog - it is not ARM native but works very well and has many language extensions.
My first (and primary) experience with APL was PortaAPL for mac. It was quite nice, and had a few hooks into some of the mac stuff such as quickdraw. The Iverson book was indispensable. PortaAPL required a 512K Mac which pretty well dates it. Unfortunately it was bought and folded in to STSC APL*PLUS who really didn’t care about Macs; it languished though supported for awhile by the PortaAPL people. There were a couple of others, but between lack of time and limited funds, I wasn’t able to try them, and for a long time there didn’t seem to be any mac versions at all. Open source offspring such as j substitutes letters and words for the APL character set, which I found jarring and hard to read.
I’m hoping to start playing with APL again because of the free dyalog version. Currently dithering between that and starting on Abelson’s Turtle Geometry book with Logo to see if I can manage to make it to the general relativity chapter.
For anyone wanting a taste of APL and it’s power, dyalog has a site with tutorials and a few walk throughs of short programs, and there’s a youtube video with John Scholes’ classic demonstration of writing Conway’s Game of Life in APL, animation and all.
I used APL when I worked for IBM as a pre-university employee in 1977. Loved it. Closest thing to a write-only language I’ve ever encountered. I remember writing a histogram-plotting program in one line. Ah, nostalgia.