I loved my HP calculators. I used them in college in the 80s, and grad school in the early 90s. Mostly HP15, 41, and 42. My last 42 is sitting in a drawer nearby, with a relatively fresh battery, and it works well.
I recall writing "programs" that performed some of the calcs I needed in the physics curriculum. I also recall being amused that I could calculate 1/3 (or 1/7) and add it to itself until I got (nearly) 1. From there this led me to study what fixed and floating point were, and think about the implications for the code I was writing (precision, truncation/roundoff error, etc.) to do longer calcs.
This eventually led me to skipping a postdoc, and working in the high performance computing industry. Where I am today.
I have the hp 41 cv app on my iPhone and it's fantastic. I paid once many years ago and have never been asked to pay again. A great group of enthusiasts keep it going.
That said, I've had recent occasion to do some programming for celestial navigation on a handheld- and the TI is a lot easier to use for that.
I have an HP-41CX+ app. I think I was using a free or entry version and I mentioned it in a review so the author sent me an upgrade to the full CX+ version. It's pretty great although it's complete overkill for me. It obviously lacks the feel of the physical calc but mine died years ago.
There's a good HP-42 app as well although I'm just more used to the 41 so that's what I use.
I credit the HP-41CV I had in in high school for growing my interest in programming. Through college it was an HP-48G. My father-in-law recognized my love for these devices later by giving me his old HP-35, complete with manuals and a couple accessories.
One of the more interesting accessories was his special HP-35 hardcore looking security lock. You would securely bolt the base of the lock to your desk, place the HP-35 inside, and connect and lock the cover with a key. Precious device back then!
I had a Radio Shack scientific calculator about that same timeframe. It was stolen during a lab. I then bought a 32Sii. Just wanted to thank the thief, as I likely never would have been a lifelong RPN user.
I got a TI to go off to engineering school because HPs were still a real budget buster. As I recall, a scientific TI calculator was still about $200 in 1975 dollars.
But calculators were dropping quickly in price and a couple of years later I was able to pick up a discontinued HP-55 which I used for years until I picked up an HP-41CV with financial pac for going off to business school. (I probably had one of the horizontal format HP RPN calculators somewhere in there too.)
I recall writing "programs" that performed some of the calcs I needed in the physics curriculum. I also recall being amused that I could calculate 1/3 (or 1/7) and add it to itself until I got (nearly) 1. From there this led me to study what fixed and floating point were, and think about the implications for the code I was writing (precision, truncation/roundoff error, etc.) to do longer calcs.
This eventually led me to skipping a postdoc, and working in the high performance computing industry. Where I am today.
They were/are awesome tools.