There are unfortunately very few options today, and in 2022 things only seem worse. Regular stock of HP 35S and 12C models has dried up in the last year, this is hopefully just due to pandemic and semiconductor shortage nonsense and we will see a return of these to production. Perhaps if we’re lucky maybe we’ll see something this year for the 50th anniversary of the HP-35.

HP 35S

This is my daily driver, it’s not without it’s issues but it generally does it’s job well and has a really nice keyboard. Integer features severely let this calculator down, working with or juggling outside of base 10 is too clunky and unusable in practice. You should be able to pick one of these up new for €60-90.

HP 12C

If you search for a RPN calculator this is probably what will show up. It’s part of the Voyager series of calculators, there was a 10C, 11C, 12C, 15C, and 16C. This 12C is the only one that has stayed in production and provides financial functions (this was the shit pre-excel). If you get one today it’s an ARM machine emulating the old hardware running far faster.

I’ve had a few of these modern 12C’s and the keyboards are decent, but they are hard on batteries (like seriously), and also far more delicate than they seem. They don’t do well being thrown in a front pocket of a work bag. So I’d put these in the retro toy category. Also about €60-90.


These are small-batch high end replica’s of old HP’s (they do some new spins on old hardware too). They’re not cheap, but in my experience they are not overpriced either. You’ll want something from these guys eventually but not your first RPN. With taxes in your hand about €140 for a DM16L, but a good condition used HP 16C would be at least €250.

The build quality of the case, buttons and everything in general is premium. They’ve also done a great job porting to modern low power MCUs.

PX16C / PX15C / Paxer

I wont beat around the bush, I don’t own one but also I really don’t like these and they rub me up the wrong way. It’s a very nice story of a guy making his own clone of a HP Voyager. But it’s built on dogshit old power hungry 8-bit AVR chips (it’s an Arduino groan). If this was open source I’d be more enthusiastic, but as it is it’s basically a shit imitation of what SwissMicros have been doing for years (with an ATMEGA, again seriously?). Not cheap either, $55 before shipping and taxes for a circuit board with a LCD some tact switches and an AVR. Adding EU shipping and taxes you’re at over half the cost of a SwissMicros for a janky and chonk DIY device that’s not open.

I really wanted to like these and get one (or a few) but the cost is too high for what it is. $55 (kit) + $25 (shipping) + $18.40 (import tax), guts of $100. It should have been entirely open source with PCB gerbers available and a “buy me a coffee” link.

WP 34S

A HP 20b or 30b with with firmware reflashed. This open source firmware is extremely capable but is pretty complicated and vast. The underlying hardware of the 20b and 30b is supposedly the same apart from colour and the keyboard quality. However I did buy a 30b and converted to 34S and the keyboard is so so awful I wont use the calculator at all, so god knows how bad the 20b is. The features on the WP 34S are great though. Needs a set of keyboard overlay stickers, and making your own programming cable is very easy. I think my total cost was around €85-90 for new old stock 30b plus 2x vinyl labels, already having the programming parts lying around.