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[personal profile] mmcirvin
If I recall correctly, [livejournal.com profile] plorkwort managed to obtain a Curta rotary calculator a while back. If you are not so lucky, you can use this Curta simulator (Flash 6 required). There is also a 3D version, but it's frustratingly tricky to manipulate. There is a manual online but since you can't damage the virtual Curta, it's interesting to try to puzzle out for yourself how to do multiplication and division of multi-digit numbers.

Apparently Curt Herzstark designed this astounding machine while he was a prisoner at Buchenwald—the camp commander wanted to give one to Hitler as a victory present. But Herzstark was liberated and the first Curtas were built after the war. Hand-cranked rotary calculators that use a similar principle go back to the 19th century (and have antecedents in the 17th), but one that you can hold in your hand is something else again.

Date: 2005-01-31 12:13 pm (UTC)
From: [identity profile] doctroid.livejournal.com
Prof. Karl Kleine found this picture in an article about use of calculators in German schools. Guess what those boys of age 10 to 11 have in their hands???

... fnarr ...

Date: 2005-01-31 07:17 pm (UTC)
From: [identity profile] mmcirvin.livejournal.com
The Odhner-style rotary calculators all have four things:

- An accumulator, with a wheel for each digit coupled by carry mechanisms

- An input register that determines the number to be added to, or subtracted from, the accumulator with each turn of the mechanism

- A carriage that shifts the relative place value of the accumulator and input register

- A counter register that counts turns of the crank, shifted by the place value of the carriage; in the better models this also has a carry mechanism

With just the accumulator, you can do addition and subtraction; the counter and carriage are what allow multi-digit multiplication and division without having to write down or remember intermediate steps.

In an Odhner machine the carriage is a typewriter-like linear thing that slides parallel to the axis of the crank. The main thing that allows the Curta to be so tiny is that its place-value-shifting carriage is circular, swiveling about the axis of the crank; the registers are wrapped around the circumference, and the input register digits have linear input transmitted through helical shafts. The amount of miniature precision machinery required to manage all that is mind-boggling, and, even staring at those disassembly photos for quite a long time, I still don't understand how most of it works.

Date: 2005-01-31 07:24 pm (UTC)
From: [identity profile] mmcirvin.livejournal.com
For extra credit, identify the equivalents of all of the above in a modern microprocessor.

Date: 2005-01-31 07:38 pm (UTC)
From: [identity profile] mmcirvin.livejournal.com
...I'm beginning to see how the setting register and accumulator work, at least. The helical shafts only transmit to the visible setting dials; the important shafts are the inner series of transmission shafts, where each setting lever shoves along one of those tiny five-toothed gears that provided the inspiration for the Curta logo. The strange multi-layered rotor with the elaborate pattern of teeth is what serves the role of the Odhner pinwheels, making each transmission shaft advance to a degree depending on the five-toothed gear's vertical position.

Date: 2005-01-31 07:50 pm (UTC)
From: [identity profile] mmcirvin.livejournal.com
This article from 1952 (http://www.vcalc.net/cu-pe.htm) does a really good job of explaining how it works, with nice diagrams, though there are some surreal OCR errors in the Web page.

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