New mobile device

I recently purchased a new mobile device. It arrived in the mail yesterday.

It's portable; it can perform all sorts of floating-point calculations; it can store numbers; it's touch-operated; it will operate for weeks without needing to be plugged in.

On the minus side, it weighs nine ounces (almost twice as heavy as my iPhone), and it's kind of slow, and its display is pretty small.

Still, it's sleek and stylish and elegant.


It's entirely mechanical.

Yep, I've acquired a Curta.

For those unfamiliar with it:

The Curta is a hand-cranked mechanical calculator, designed just before WWII by Austrian inventor Curt Herzstark (and redesigned during his time in the Buchenwald concentration camp); about 150,000 of them were produced from 1947 through 1970.

It looks very much like a short pepper grinder made of black and/or gray metal and/or plastic. (You can view photos and drawings on the abovelinked Curta page, or keep reading for some links to videos.) You set an input number using sliders on the outside of the cylinder, and then you use the crank on top to add the input number to, or subtract it from, the output number on top. Through a clever shift mechanism that makes it trivially easy to multiply the input number by a power of ten, you can very easily multiply or divide multi-digit numbers, and you set the decimal point manually. You can even calculate square roots (PDF) via a complicated algorithm, though I don't entirely understand how that works.

Mine is a Type I Curta, serial number 24310, mostly likely made in the early 1950s. It's black metal; I like the look of the older ones a little bit more than the gray plastic later ones, although the Type IIs had more digits and thus higher precision.

Thanks to Jeremy F for telling me about them in a blog comment five years ago, and to Lisa H for letting me try hers.

I've wanted one ever since I first heard of them, but they're very expensive, and I couldn't justify the cost. But it recently occurred to me that they're only getting more expensive over time, so after much waffling, I finally decided to buy one.

It's pretty awesome. I'll be happy to show it to anyone interested; in the meantime, if you're interested, you can watch online videos, such as a general demo (7 min), a demonstration of multiplying √5 by itself (1 min), and a demonstration of another method for calculating square roots (6 min) (I used this method to calculate √5 and √7—nifty!).

If you have a VRML viewer, you can try out Yet Another Curta Simulator, a complete virtual working model; there's also a video showing assembling the virtual model (2 min).

There's also a pretty good Flash-based simulator by Jan Meyer. It doesn't give you quite the same feeling as holding the device in your hands and turning the crank, but it does help in understanding some of how certain aspects of it work.

One Response to “New mobile device”

  1. BC Holmes

    That sounds really interesting. I hadn’t heard of these things.


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