The fundamental things Or, a cos is still a cos

The fundamental things Or, a cos is still a cos
These days we are all used to computer technology, but there were times when it was new and and really cutting edge. Looking back, the Hewlett Packard HP35 was an iconic calculator with its reverse Polish notation.

This year has seen the 45th anniversary of the introduction of the Hewlett-Packard HP35 calculator. And the 10th since HP built its “tribute” or “retro” HP35S to mark 35 years of the ‘35.  It’s something of a cliché to say, “It’s very difficult to convey the impact the HP35 had on its first introduction,” - but it’s nevertheless true. The HP35 enabled trigonometric, logarithmic and exponential functions to be evaluated on a handheld device for the first time.

Prior to that (and for some time thereafter, for those who could not afford the HP35’s $395 price tag* at launch) even a simple calculation required the use of methods that are largely lost to history. Need to work out a phase shift, a resonant frequency or an AC impedance? Reach for the slide rule or trigonometric tables. Those who had access to a computer – perhaps working at sites that had a mainframe – could program their computations and submit them for batch processing, which was only worth doing for longer and more complex tasks.  Mainframe computers still lived in air-conditioned suites with an operator priesthood guarding access; if the priesthood permitted, you might get remote access to a “real time” access via a Teletype terminal, on which you could type in individual program statements and get transcendental functions evaluated. This was also the era of the minicomputer, although they were not particularly user-friendly either. Even if they had emerged from the air-conditioning, they still called for a ‘programming’ approach.

So, HP’s hand-held unit with its fixed functions – each was a ROM-coded routine that guided operation of a separate arithmetic IC, this was not an antecedent of microprocessor-based devices – became an instant talking point wherever it appeared, and HP sold many times its initial market prediction. (If you have never handled one, there are fully-functional depictions on-line).

But that was then, and this is now. The intervening years have brought the PC and all its derivatives, and the migration of compute power to both extremes of the smartphone at one end, and the cloud at the other. There is, surely, no place left for the “electronic slide rule”? You can argue that point, though.

If you have a complex task to carry out – such as, perhaps, designing a filter – there are many on-line resources that will provide a pre-packaged, user-friendly, accurate and probably free solution. Or a plethora of desktop PC or even smart-phone app options. For that one-off calculation, there is the scientific calculator in Windows; or in the Linux distribution of your choice; as an app; or Google will directly return the value of most functions you might ever need.

But if there is any single thing that keeps the idea of a dedicated device alive, it lies in the ergonomics, and in having a simple function immediately to hand to answer a simple need. If you choose to have one today, the obvious route will be an app from the Apple or Google Play stores, of which there are many (and yes, you can have the authentic Reverse-Polish-Notation experience!). The HP calculators themselves had and have, “nice buttons” with a reassuring action. With some learned familiarity with the key positions, you can sit it on the bench and have most of your attention on the primary task: and be confident that your key-presses are accurate. For all the compute power and sophistication, using a smart-phone touch screen for the same purpose is not exactly the same user experience.

Do you keep a scientific calculator on the bench or in a drawer? Is it even a ‘legacy’ model? Or has the all-powerful smartphone mopped-up that function in addition to all its other conquests?

As an afterthought, there is another numerical link from the HP35’s debut to the present, besides round-numbers of years. Its chipset, by Mostek or AMI, was built in PMOS of around 10 microns feature size. Three complete orders of magnitude through Moore’s Law shrinking, brings us to today’s state of the art CMOS – now, it’s nano not micro-metres. However, the chips were reportedly clocked at a mere 20kHz: then as now, power saving and battery life were top priorities.

* around £165 in the UK; as an order-of-magnitude calibration, more than a month’s salary for a young engineer. The $/£ price ratio doesn't entirely match the broader currency conversion of the day, but that is also an echo of a bygone age.

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