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From Sinclair Scientific to HP-45 - What a Relief!

Posted by Les Bell on 22 Oct 2005, 3:20 a.m.

In 1974, I was a student, studying Cybernetics and Instrument Physics, at the University of Reading (UK). Pocket calculators were fairly new and expensive, and the HP-35 was the only scientific pocket calculator. One of our labs had one, bolted down in its security cradle, and was an absolutely amazing device to us slide-rule users. Way out of my price range, though.

However, Electronics Today International magazine ran a special offer for readers: a Sinclair 4-banger calculator in kit form, for only GBP14.95. I was hooked straight away and ordered one. I built it in a couple of hours - there were only one or two IC's and a few discrete components to be soldered to the circuit board. It worked like a charm, and that night I used it in my holiday job as a barman, to add up a customer's order. The customer was amazed, and offered to buy the calculator. I can't remember whether I sold that one or not, but I remember buying quite a few kits and selling the completed calcs to people, making something like GBP5.00 on each one!

The Sinclair Scientific

Later that year, the magazine offered something much more interesting - the Sinclair Scientific, in kit form. I think the price was the same, or very close. I immediately ordered one - I guess I was far from the only person to do so, because there was an immediate backlog and it took ages for the kit to arrive. It finally did, so I set to work, and a couple of hours later, inserted a battery and switched on, expecting to get to grips with the calculator's strange RPN system. Only. . . nothing. Dead display.

I took it apart again and checked for dry joints, but everything looked fine, so next day I took it into the electronics lab where I could put a 'scope onto the beast's innards. It didn't take me long to discover that there was no output from the clock chip, but I couldn't figure out why. Dejected, I put the dead calculator into my jacket pocket and trudged back to the Hall of Residence where I lived. Meeting a friend just inside, I shared the bad news about my new toy, and pulled it from my pocket to show the dead machine - only when I switched it on, it worked!

I tried a few calculations and got the right answers, but within a few minutes, it died again. It took me a few hours of head-scratching to realise that what had revived the calculator was exposure to the cold night air in my jacket pocket. As a test, I put the calculator into the ice-box of a refrigerator for 30 minutes, and sure enough, it came to life again.

A phone call to Sinclair Radionics confirmed that they would fix it under warranty - apparently TI had supplied a batch of chips that were temperature-sensitive and would only work when cold. However, I had a Control Systems course to get through, and for the next few weeks I worked on Routh-Horwitz Stability Criterion and similar problems by getting all my numbers organised on paper, then nipping into the kitchen to retrieve the calculator and number-crunching until it warmed up and failed. Then back into the ice-box it went!

By early 1975, I'd got the Sinclair Scientific repaired, but the limitations of its RPN implementation were becoming very obvious. With no x<>y function, a lot of calculations required writing down and re-keying intermediate results, and (from memory) a 3-level stack and no memory was very constricting. By now, the HP-45 was out, and I'd got a brochure from the nearby HP UK head office in Newbury. I had to have one, so I worked all through the Easter break to save up the GBP128 it would cost.


As soon as the holiday was over, I headed to London and bought the HP-45. With many more functions, nine (9!) memories and a proper 4-level stack, the '45 was a huge relief after the Sinclair. I also bought the HP-45 Applications Book, which was full of keystroke sequences for all kinds of (to me) arcane calculations. My favourite was the weekday routine - I used to regale my non-numerate friends with the day of the week on which they'd been born. Most importantly, Routh-Horwitz and similar calculations were much quicker than with a slipstick!

I can still remember the style of the HP-45 Owner's Handbook: extremely well written, with humorous examples, use of spot colour for the "gold" key, etc. In fact, it was the quality of the HP calculator manuals that inspired me to pursue a career in technical writing, and when Electronics Today International magazine advertised for an editorial assistant later that year, I applied for the job. The publisher wanted a sample of my writing, so I wrote a review of the HP-45, and I got the job. After a year in London, I was sent to Toronto to launch a Canadian edition of the magazine, and while I was there, I was able to acquire an HP-65 at a discounted price, as the HP-67 was just about to be launched. Eaton's department store also had a large stock of HP-65 Solution Pacs they wanted to quit, so I picked them up for a song.

From Canada, I was promoted to Head Office in Australia, where the '65 disappeared, possibly stolen. It had some LED segment failures, and I was about to send it to HP for repair anyway, so I contacted HP and asked them to watch for it being returned, but it never surfaced. My employer provided an HP-67 as a replacement, but I left soon after, and although they offered to sell it to me cheaply, I turned it down, because I knew the HP-41C was on the way and would in many ways render the '67 obsolete.

Since those early days, I've travelled the world, lecturing and consulting, and I picked up a small collection of HP calculators - often buying them duty-free at Singapore airport. I still have a 41CV, 41CX, 82143A printer, 82104A card reader, lots of modules, a 16C, a 48GX and 82240B. I don't really have any professional use for them these days, but they're wonderful learning tools and toys, and I fondly remember the influence those early calculators had on my career direction.


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