for a longer time I was searching for a good and programmable calculator for my Android tablet. After trying quite a few emulators, which either
does not use the space on the screen very well (my tablet is a 7" one) or need to have the original calculator for legally owning a ROM image or
simply were better in design than usability I first came across the HP42s-page on wikipedia, which states something like "best calculator ever made".
Then -- via a wikpedia link list -- I found Thomas OpenSourced (YEAH!), free (YEAH!) and independently implemented (YEAH!) Free42, which solves
all my previous "problems" in one go. Together with the manual for the HP42s this was EXACTLY for what I have searched for.
Then -- I think it was while I am was surfing the net for HP42s programs I found that at HPmuseum.org -- a posting, that Michael and David were
prototyping a DM42L (the landscape version).
From then on I was checking for news around the DM42 regularly and in the moment the DM42L was changed for a DM42 (portrait version) the
DM42 mutated from a "oh,intersting" to a "I must have that"-item.
I owned a RPN-calculator never before and only one programmable calculator (Casio FX602P) in total. But I know "kinda RPN" for playing around with LISP and RACKET.
I think RPN as a notation system has a comparable reputation as the vi/vim editor: As long as you don't have touched them you remain a victim of what other say about them: old-fashioned, old-school, steep learning curve, awkward and somehow quirky.
As soon you learned them you start to love them and finally you are thinking: "What the hell I did all the years before?"
Needless to say that I love RPN as I love vim...