The rarest HP calculators are one-off items, such as mock-ups of proposed new models, or test versions made to help at the design stage, or handsets which look like the planned calculator but have to be plugged into a box of electronics which contains the actual programming being tested. None of these are real calculators, though, so most collectors leave them alone. They do not really count! (Or should I say they really do not count? My thanks to Frank Wales for pointing this out to me!) Still, some people would give an arm and a leg for one - for example HP thought of following the HP-01 LED watch with an LCD version to be called the HP-02. I don't know if any HP-02 mock-ups were ever made, but I know there are people who would try to get one the same way as the man in the parable who sold all his worldly possessions to get the pearl of great price.

The next rarest are working prototypes. HP sometimes design a product, make a preliminary batch, then decide not to put it into commercial production. In the case of calculators, the HP-95C is the only example I know where this happened, and, again, there are collectors who would (nearly) kill to get one. Still, if the product was never sold to the public then most collectors - sensibly - see no reason to try getting one for their collection.

Next come some very rare models which were sold to the public, but did not sell well. The HP-01 calculator watch is one of the rarest - HP treated it as a luxury product and sold it through selected jewellers and watch sellers, not through calculator dealers. It was very expensive for a watch - particularly the gold model - you could get a Rolex for the same sort of price - and it was introduced shortly before red LED (Light Emitting Diode) displays were replaced by the much more efficient, less battery-hungry, and permanently visible LCDs
(Liquid Crystal Displays). So, it did not sell at all well. If you can get one, well done, but many calculator collectors do not bother with it, since even HP treated it as a watch, not a calculator.

The three different HP-94 handheld computers are very rare too. They were designed for companies to buy in bulk, to be programmed for special purposes such as stock-keeping. There was significant interest in this model, but each interested company initially bought only a few, to write and test their programs, before buying in bulk. By the time the companies had their programs ready and were ready to buy in bulk, HP had decided the HP-94 was not selling well enough, and withdrawn the product! Actually, the HP-94 was not made by HP - it was made for HP by Fujitsu, and only had an HP label. So, it was not
really an HP product, and is ignored by most collectors, except those lucky enough to have got one.

Another class of rare model is the "special". For example the HP-97S was an HP-97 slightly redesigned and with an add-on box which made it possible to connect it to electronic equipment to take readings or control that equipment. Many collectors would treat this as a "special" version of the HP-97, and would not bother to try to get one. A different example is provided by special versions of calculators which just have an extra logo on the case. A batch of HP14B and of HP32S calculators like this was made for the 50th anniversary of HP. Similarly, a special run of HP28S calculators was made at the introduction of the HP28S, with a logo commemorating the 100th anniversary of the American Mathematical Society - these were presented to mathematicians at a conference organised on this centenary. (See the separate article in a recent DATAFILE by Bill Wickes about the introduction of this model.) There is nothing special about these calculators apart from the wording or pattern of the case, and some collectors want these for their collections, but most are not bothered.

With some models, HP make a few calculators which work as normal but are in a transparent plastic case, not the normal HP black (or dark green or dark blue) plastic case. These are designed to let people see the insides of the calculator - maybe to let them see how well it is made, and how much gold plating goes into an HP calculator - no doubt justifying its high price. It is nice to have one of these, but they really are a "special", not a different model, so most collectors do not feel a vital need to have one.

Well, that about covers the rarest HP calculators - and at the same time gives you an excuse you can give in each case for not having one! That was the other subject of this article - why you need not feel
deprived if you can not get these rarities. In a future article I shall look at some other HP calculators which are hard to get, but definitely are worth trying to find.

This article is part of the WMJARTS file. This file contains a series of articles written by Wlodek Mier-Jedrzejowicz and published in DATAFILE, the journal of the HPCC. The article was reproduced with permission of the author.