I tried the HP35s of a friend for a few days. It is globally a nice RPN calculator and not too expensive for starting. But I don't want to get one because this calculator have a quite long list of known bugs [1] that have been sitting there for more than 10 years now, and HP hasn't fixed anything yet!

If you are a grown-up children like me and just want a pretty expensive toy, I can recommend the SwissMicros DM42 [2] (I'm not related to them in any way, just a happy customer). The made an adaptation of the HP42s for the modern world: «34 decimal digits of precision, with exponents ranging from -6143 to +6144», based on the excellent Thomas Okken's Free42 [3], big and nice screen, USB connection for loading/saving programs, save and restore of the calculator state, and so on!

And being based on Free42 you can get the emulator on your phone and share the programs with the calculator. You then have the same "calculator" everytime with you, no need to get used to another program/interface on your phone.

[1] http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cg... [2] https://www.swissmicros.com/dm42.php [3] http://thomasokken.com/free42/

I also use clac on my desktop (https://github.com/soveran/clac). It's a line-oriented RPN calculator like Unix dc, but it shows the stack dynamically as you type. I have a long-term ambition to port it to a physical calculator - either my own design or one like the Numworks or a SwissMicro (a recreation of the HP-42s).

My trusty companion, when my HP 48G isn't with me, is my 1987 HP 42S. It has been on my desk for around 2 decades.

https://en.wikipedia.org/wiki/HP-42S