The Curta Mechanical Calculator

And now for something completely different.

There was a time, children, when computers didn’t exist. And when they did exist (hello, Colossus) but were far from commonplace. People getting telephones at home, or even, gasp, televisions were new and exciting events. The radio was made of wood, and rather more listened to (perhaps due to the absence of TV, or because the people had better accents).

But what about calculators? Think of a calculator and you think of perhaps an app, or an electronic calculator, whether a simple everyday one or a swankier scientific version.

But what if those don’t exist? Well, you can work it out in your head.

Or you could use a mechanical calculator. The one pictured is the Curta, designed by Curt Herzstark. Born in 1902, he was an Austrian and son of a Jewish father. He’d completed the Curta’s design by 1938 but the Nazi annexation of Austria rather put the kibosh on production plans. He was ordered to make devices for the German army, until he was arrested in 1943 and sent to a concentration camp. Despite the less than ideal circumstances, Herzstark was able to redraw the designs from memory whilst in the concentration camp.

The mechanical calculator he created is similar in dimensions to a cylindrical deodorant can, albeit perhaps 2/3 the height and with a slightly larger diameter. It comes in an airtight two-part container.

I am not an engineer (the people who used the Curta perhaps the most), or a mathematician, but I must admit I found it to be not very intuitive (I’ve provided links to a few helpful Youtube videos at the end of this article). There is a series of movable switches running around the lower part of the cylinder. On the top is a handle that can be rotated either in the up or down position, with a separate ring that can be rotated (with the top part raised, this resets the device).

Turning the handle is curiously satisfying, like grinding a pepper mill full of numbers.

It turns out the switches on the lower part are for integers to add, subtract, multiply or divide. Turning the handle in the down position is for addition, in the raised position it subtracts. The number currently worked upon is indicated once an initial calculation (addition) has been made. So, the switches might be flipped to 1 0 2 4 at the bottom, the handle turned, and 1024 shows up on the top. A second turn adds the same again, yielding 2048. Multiplying small numbers is simply a matter of repeated additions.

For a larger multiplication, such as 2048 by 299, the upper part of the calculator is raised, and rotated so that the 2048 at the bottom (movable switches) is entered in the hundreds rather than units. This adds 204800 to 2048 (so, a multiplication by 101). Repeated twice is multiplication by 301. The top part is raised again and returned to the units, and the handle raised to the subtraction position. A double rotation removes 2048 twice, giving us 612352. As well as this, correct, answer, the multiplication factor (299) is shown on the upper part (in a silver rather than black area). [Experimentation reveals that if you subsequently alter the switches number, this is not taken account of. So, doubling to 4096 and adding once increases the count to 300].

Anyway, it’s an interesting little thingummyjig, and I thought people into engineering, history, or creative writing might be intrigued to learn about a calculator that doesn’t need any fancy electricity to get its business done.

Youtube links: https://www.youtube.com/watch?v=_KomtGXzT3o

https://www.youtube.com/watch?v=loI1Kwed8Pk

https://www.youtube.com/watch?v=fhUfRIeRSZE

Thaddeus