That seems like a long time, but man this calculator is nails, the best ever, IMO. 25 years is not a long time to own something, necessarily, but to use it on an almost daily basis for that long.
All hail the fantastic HP 12-C!
I didn’t understand the power of RPN calculators when I was in high school and college. What a mistake that was. I love using my HP and can’t go back to traditional calulators. One time I went to the store at 10 pm to get batteries for my HP when it ran out because I couldn’t stand to use a normal calulator.
HP should sponsor events at high schools where they demo their calulators to math and science nerds.
You’re lucky; they still make the 12C. I’ve got a 15C. I don’t use it every day, but if it ever gives up the ghost I don’t what I’d use then.
I have the official HP 12C and 15C apps on my iPhone.
And an HP48GX. 
I have a HP 48G that I have used almost daily since 1995 (16 years!). I would be lost without it.
Big deal. Are you expecting it to wear out or something? You crunch some really heavy figures? Or maybe you come up with some especially irrational numbers? Oh, no, wait–I know: You just calculate so fast that most calculators would explode. That’s it, right?
I’ve got some sort of HP RPN calculator (not sure which one). Got it sometime around 1989-90, used it to subtract the checkbook, mostly. It’s still running. On the same battery.
My HP15C was stolen from my desk drawer when I was in grad school. I still haven’t gotten over it.
This Android app is a decent replacement, though 
(Missed the edit window)
On the PC, I can recommend XCalc. There’s also a pretty good 15C emulator which comes for Win, Linux and Mac OS
Og have mercy on the young’uns who’ll probably never learn to use a real calculator (i.e. with RPN notation)
Sorry if I offended you.
HP48GX for the win! I’ve had mine since '94, I think. I don’t use it quite every day, but close to it.
On the road, I use an HP48GX emulator on my Android phone. I miss the clicky buttons, but everything else is the same. And it fits in my pants pocket.
I was enamored with RPN almost instantly. It mapped exactly to my internal thought process: you’ve got a 5, and you’ve got a 6, now add them together. Infix never made sense to me since you haven’t collected all your arguments by the time you decide to operate on them.
!! I forgot to put in the :D. (That was a joke.) I congratulate you on your devotion to the 12-C!
I myself am more of TI-84 kind of person–but I won’t say anything about that.
15-C owner since 1982. Still works, even though the back is scratched up, the brushed Al covers loose, and the little plastic case that holds it is splitting on the edges. The only thing about my calculator that doesn’t match everyone else’s stories is the need to replaced the batteries every three-to-four years. I must be on my 7th or 8th set now.
That and my still-working SVEA 123 cookstove I bought back in 1971 (for $10.95 at Fed-Mart) are two of my most cherished processions.
I suppose I could replicate one electronically along with a display, but the keyboard itself would be the most difficult to reproduce. Every other calculator I tossed because the keys failed, but not the HP-15C’s.
I learned to use a calculator on an adding machine. Those work in much the same way as RPN. Using the 48GX when I got to college was a breeze.
I bought my HP 16C scientific in 1982. It sits on its little wooden stand under my monitor, and I use it nearly every day. 29 years old and every bit as usable now as then. Not many other high-tech devices can make that claim!
My 11C is about 22 now - yeah, these are great little machines! In one of my alternate lives as a bazillionaire, I want to copy them, only with titanium cases and sapphire windows. I think they should be archival touchstones for future generations’ collective quantitative consciousnesses, too.