It’s about time I introduced the first Hewlett-Packard calculator I ever bought. Unlike the previous calculators I’ve shown (Litton Royal 5T, Casio SL-800, Casio ML-81) which were replacements obtained long after the originals had been lost or thrown away, this is the actual calculator I purchased and used back in 1988. I can’t remember the cost, but it must have been enough that I also splashed out on the deluxe leather case to protect it. These days they go for about $150 on eBay for one in good condition with manual and standard case.

This machine is a killer scientific (and business) calculator. It not only has your usual scientific functions – trigonometry, hyperbolics, logarithms, powers – but also probability and statistics, date arithmetic with both normal and 360-day calendars, different base arithmetic (decimal, hex, octal, binary), and Time Value of Money (TVM). It’s not programmable, but instead had a powerful Solver function – enter some formula with variables, enter (all but one) values for the variables, and it would solve for the unknown. There’s even a menu system so that the buttons stay simple visually and are not too overloaded. Peculiarly perhaps for an HP calculator, it used algebraic entry (spot the parentheses and the equals button) and not RPN (Reverse Polish Notation). It even printed via infra-red to an external HP 82240A printer, if you had such a wonderful beast (I didn’t). It was the “do-everything” calculator of Hewlett-Packard’s range at the time, and it hasn’t been equaled since.

In HP collector terms, this is a Pioneer calculator. Others in the Pioneer range (all of which I’ve now bought to fill out my collection) are the 10B, the 14B, the 17B (and its successor, the 17BII), the 20S, the 21S, the 22S, the 32S (and its successor, the 32SII), and the 42S. (B stands for Business, and S, Scientific, although the 21S is a “Stat/Math” calculator.) All have the same shape, have the same keyboard layout (although the colors and legends on the keys were different) and took three chubby Duracell LR44 cells (or equivalent). Although the display size was the same across the range, the display itself varied from a single line segmented LCD display to the two-line matrix display on the more expensive ones, like you see here.

The Solver function was available over several calculators, including the prodigious top-of-the-line clamshell HP-19B (and 19BII). Consequently HP published several additional advanced manuals for these calculators to help you with Solver calculations in various vertical markets. For the 27S there were step-by-step manuals for personal investment and tax planning; real estate, banking and leasing; business finance and accounting; marketing and sales; and technical applications. Even today, these manuals are a great embodiment of formulas and how to perform calculations to minimize the error bars.

I bought it at the point in my programming career when I was starting to develop advanced trading software for swaps and similar financial instruments, hence doing a bazillion present-value type calculations. The date calculations and TVM helped enormously here to check my code and my results. Whereas others around me used HP-12Cs, I plugged away with my trusty 27S.

It really has to be my most favorite calculator ever. I still use it, albeit infrequently now. It really is a fabulous machine, even though it’s now 24 years old.

For your jaunt down memory lane today, I present another calculator from my collection: the Casio ML-81.

On the one hand it’s a four-banger with memory, but on the other it plays music! Click the picture to expand it, take a look at the keys really carefully and you’ll see that they are marked Do, Re, Mi, Fa, Sol, La, Si, etc. When the little slider switch top right is in the treble clef position, the calculator will ding every time you press on of the number keys. Not only that, but if you do a calculation, it’ll play the answer to you. Now admittedly the notes are entirely artificial, electronic, and ting-y, but they’re there.

Not only that, but it has clock functionality as well. So there’s the current date and time (you can see when I took the photo, for example) which chimes on the hour every hour, stopwatch and timer functions, and there are two alarms. And, when in the awesome treble clef position, the alarms will play a little melody when they expire. Alarm 1 plays the beginning of Frühlingslied by Mendelssohn and alarm 2 plays Traumerei by Schumann. (The timer plays a tune when it reaches zero: Schubert’s Moments Musicaux No. 3.) All pieces are twenty four seconds long.

So, why do I have this calculator? Apart from it being an entirely awesome piece of consumer electronics, that is? To be honest I bought one back in the mid-80s just for the fun of it. It was cheap enough that it was just a spontaneous purchase: I saw, wanted, bought it. Probably in some electronics shop on Tottenham Court Road, if truth be told. I even used it as my wake-up alarm instead of a boring old clock for a while. And then my flat was burgled one day and they took it along with my hi-fi, CDs, and other stuff. Then, about five years ago, maybe more, I spotted one in an auction on eBay (NOS - New Old Stock, as they say) and bought it for $50. That’s the one you see here. I keep it out on my bookshelves (in its cover) and it still merrily chimes the hour.

(There were a whole bunch of different Casio calculators from the 80s that have clocks and tunes, some of which I own. I’ll do another post showing some of them.)

OK, kids, gather round old Gramps as he shows off the first calculator he ever owned. He got it as a present for passing his O-levels. (Actually, even if I’d had the calculator prior to taking my O-levels, I wouldn’t have been allowed to use it for the exams. Unlike math tests today, It was slide rules only in those days.) Are you gathered round? Here it is, the Litton Royal Digital 5-T from 1973.

Just look at that beauty. It takes 4 AA batteries which last, oh, at least an hour. Fully loaded with those double-As, it weighs 9.9 oz (280g) – for comparison, an iPhone 4 weighs 4.9 oz (137g), half the weight. Dimensions? Glad you asked: 5.8" × 3.5" × 1.4" (or, for those of a metric persuasion, 147mm × 89mm × 36mm). This is one big-ass calculator.

If you look carefully you can see that it has light-emitting diodes (LEDs) for the 8-digit display, although Litton preferred to call them “Digitron Tubes”. They are the reason the batteries didn’t last. Well, that and the fact there was no auto-shutoff. If you forgot to turn the calculator off manually, the next time you used it you’d have to put in new batteries.

Another thing: there is no zero suppression for the display. Clear the calculator (the C key) and the display shows 00000000. Suppose you wanted to know what 355/113 was. Type in the 355, you’ll see 00000355. Hit the ÷ key, the display shows 355.00000. Type in 113 and you’ll see 00000113. Press equals to see what the image above shows: 3.1415929. I mean, those zeros just ooze accuracy, no?

And that K key is, er, key. It allows you to do a set of calculations with a constant. K for konstant, amirite? Let’s say I had those measurements in inches from above and I wanted to calculate the equivalents in millimeters. Since there are 25.4mm per inch, all I have to do (actually “had to do” since I used the calculator itself for this) is type 25.4 × K to set up the constant calculation, and then 5.8 =, 3.5 =, 1.4 = to calculate the millimeter equivalents. Just try and do that with your fancy-schmancy Casio.

Despite its drawbacks, I loved that calculator. Using it was like magic; a feeling I have a hard time experiencing with any other calculator. When I first got it, I’d have fun just doing calculations. I’d compare its accuracy with my slide rule. I don’t think I’ve ever got over the sheer amazement of it working and how it could be right, time after time. By the end of the 70s, I had my degree and was earning coin as a programmer and that initial sense of wonder had gone.

As it says in my bio for this site, I’m a calculator collector. Mostly Hewlett-Packard LCD calculators it must be said, but every now and then I pick up something from another manufacturer.

Back in the early 80s, I remember buying one of these Casio SL-800 calculators for fun, a gold one. And then – because it was the size of a credit card  -- I put it into my wallet, which of course sounded its death knell after a few months. They are just not that robust. Sad to say, my original one bent and came apart and I didn’t bother replacing it.

These SL-800s really are the size of a credit card, not only in width and length, but also in thickness. Yes, like a credit card, they’re only 0.8mm thick.

This is an edge on view of the black one with a quarter alongside for comparison.

As you can see, they’re a simple “four-banger” type calculator with memory, running off solar power. Originally made from 1983/84. Without the thickness feature, these two calculators would be totally and utterly uninteresting. Because they get wrecked pretty easily, they tend to go for relatively high prices on eBay, say between $50 and $100. Mine came with the original instructions, warranty document, and slipcase box and look unused.

(For fun, and to follow on from my previous post about continued fractions, the gold one is displaying 22/7 and the black one 355/113, the first two continued fractions – not counting 3, that is – for π.)

...And mine arrived this afternoon. Just stunningly beautiful, and the picture does it no justice whatsoever. You have to hold one in your hands, weigh its heft, feel the clicks as you wind the handle, peer at the little digits.

Yes, it's a Curta Type I mechanical calculator, affectionately known as the peppermill. This one is probably from April 1964 (there's a whole lore about how to date one of these little beauties — I used the Curta, for practice) and if electronic calculators killed the slide rule, this engineering marvel was blown to smithereens by their arrival. And it's such a shame.

Essentially it's a standard mechanical calculator, with the linear carriage wrapped into a cylinder. Yeah, "essentially", indeed.

It was invented by Curt Herzstark entirely in his head while he was in Buchenwald concentration camp in World War II. After the end of the war, he put it all on paper, patented the heck out of it, and a company in Lichtenstein called Contina AG Mauren started selling them. (Sounds like a Tintin adventure, it really does.)

The Curta Type I has 8 digits of slides, an 11 digit product or result dial, and a 6-digit quotient or counter dial (the manual calls this configuration 8 x 6 x 11, with the larger type II being 11 x 8 x 15). It can do addition, subtraction, and through a clever system of raising, rotating, and lowering the carriage, multiplication and division.

Pride of place, this one.

(The manual. A Flash animation to practice with.)

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