You may ask yourself, how someone acquires such a strange fad: to collect Hewlett-Packard pocket calculators. The reasons why are really simple: [I] During studies I afforded for 500,- Deutsch Marks a second hand HP-41C, which was in strict accordance with my vision of a programmable calculator. With it I dealed problem-free with all exercises in chemistry, physics, and mathematics. [II] The good documentation of my Mollier's h,X-program for water-humid air helped as well to get an employment at EVT to program and maintain FORTRAN programs.
Very soon I was fascinated of «my» HP-41, as handy in use, it's size, and it's legendary keyboard. And multifaceted extensible with modules of only 5 Grams but the corresponding manual of 2.5 kg weight. A little marvel of technical science. I busied myself with the reasons of the ease of use, the man-machine-interface (HP holds some patents about that), amongst other things with the slightly different entry logic without parentheses. The ordinary infix notation such as 3 * 5 may -- by stipulations of logic rules -- be written unmistakable as * 3 5. Those rules had been published in 1929 already by the Polish logician Jan Łukasiewicz and are known for the easier pronunciation as Polish notation. The reverse Polish notation (RPN), used in many HP calculators, is the reversion of arithmetic operator and operants. 3 5 + 8 * for example is in the ordinary notation (3 + 5) * 8.
After the studies my fascination abided whereas my interest shifted to the evolution of those little miracle works. So my collection is grouped round the HP-41 as principal item, just to show by the difference to the predecessors and successors it's outstanding class, which was IMHO never reached again. Collecting became a little passion and so I own 94 calculators today, 23 spare for trading and barter. Almost all of them are second-hand; several went a long way with colleagues. The good restored and working calculators are displayed in two showcases, so memories of former EVT collaborators and corresponding anecdotes stay alive. That is an extra aspect of my collection.
An additional aspect is the computer-based imitation of pocket calculators on different operating systems. The imitation may feign the user interface and functionality or -- yet more interesting -- logically emulate the CPU. The idea is not new; even HP sold HP-41 simulations for the HP-71B and -48SX. Capable programmers offer at no charge emulators of HP-41, -48, and -49 for Windows among others. That sounds reasonable, first test something comfortable on the PC and next transfer it to the pocket calculator. Interestingly enough, with emulators all expansion modules work at once on the PC. Needless to say, such modules I collect too, 70 of them at current, in addition to the technical literature. Even today pocket calculators still have in many fields the right to exist besides the PC, why not directly on the PC? Just to give it a trial as help in decision-making before purchase. So HP offers [meanwhile: offered (M.)] the financial calculator HP-10BII for testing as emulation in the Internet.
A detailed description of all particulars would to exceed the limits here. If I brood your interest a little bit then have a look at http://www.hpmuseum.org. An article about RPN you found on the internal network [it was a copy from PPC Calculator Journal V9N5P26b and this snippet] together with a list of all my calculators and what I am still looking for. Or just call me if you still have some questions or like to give me your old HP. By the way, what I do is pure hobby and not -- like some other collections -- a hidden asset. A burglary here will not be worth it. Trading between collectors goes item by item (till today I know only one woman collecting HP calculators).
While writing this article I remark that my zest for sophisticated computer-based helpers, that facilitate everyday's chore, is still «my program». This shows once again at the implementation of PIRS (Project Information Retrieval System, a Lotus Notes based tool to keep huge amounts of correspondence transparent, assign tasks and maintain list of open points, it's from SOBIS).