On Sun, 29 Mar 2020 22:06:02 -0500, Charlie Hoffpauir
wrote:

Happy to see a mention of HP's RPN calculators. I'd say the best made
claculators "ever". I still have 2 HP 15C's and a 16C, all still work
fine and I still prefer them to any others. I wouldn't sell them, but
I'd bet they are worth more now than when they were new (and no, I
don't remember what they cost).

Expensive, some HPs included insertable modules for modifying their
application. I have them, better unit models (possibly not the
programmable unit above). Three HP calculators ported to a DOS
program to correspond to simulations to three popular HP RPN models.
Quick dig: Several RPNs, not all HP, just not the three HP models I'm
thinking of, which I'd have to dig deeper with some UnixDOS ported
text utilities for better search operands. Better graphic calculators
are still expensive, just not as expensive as an aftermarket Pacific
Rim facsimile, not even near some of the deals to be found there.

A couple more other earlier models, anyway.

README.V30
This file lists the changes from version 2.2/2.3 of RPN to version
3.0. RPN is an MSDOS-based emulator of an HP-29C calculator, with
extensions. It assumes an 80x25 text display.

RPN is a calculating tool written by J.I. Landman to be
used primarily by scientists and engineers. RPN is basically a
calculator, with quite a bit of power. RPN is a useful and powerful
tool for those who regularly use Hewlett Packard calculators (such
as the HP-42S, after which RPN was modeled)