Tuesday, July 28, 2009

The Curta Calculator

The Curta Calculator is an amazing mechanical device.  It was first produced in 1948 as the brainchild of an Austrian, Curt Herzstark (1902-1988), based upon work of the famous 17th century mathematician Godfried Leibniz (1646-1718). It performs addition, subtraction, multiplication and division, and with some ingenuity even more complex functions.  While Herzstark had conceived the device during the 1930s, it was actually during World War II while a he was imprisoned at the Buchenwald Concentration Camp (his father was Jewish), that he worked out the actual design of the first production devices.  After being liberated from Buchenwald in 1945 and before 1948 he finalized the design and brought the device to the marketplace. The Curta factory was located in Lichtenstein.

The Curta I has 8 slides for entering one of the operands and a 6 digit revolution counter for the other operand and an 11 digit result counter. The entire Curta I weighs only 200 gm.  There were 80,000 Type I calculators produced.  The larger Curta II, first manufactured in 1964 has 11 slides for entering the first operand and a 8 digit revolution counter, and 15 digits for the results. The Curta II weighs about 370 gm. The Type II model had a production run of 60,000.  The difference between the two calculators was primarily the number of digits of significance that the devices could handle.

The first thing you should know about a Curta is that it is small enough to fit in the palm of your hand.  It is so small, in fact, that you could not imagine a device this complicated fitting in such a small space. It has such a good feel when holding it and operating it. Curtas are sometimes called "pepper grinders" because of the similarity in looks and size. 
 Numbers are entered on the slides. A rotating crank on the top allows the input number to be added to the result. By lifting the crank the input is subtracted from the result. Rotating the top will cause the the input to be either multiplied by 10 or divided by 10 depending on the direction of the rotation.  So, with a sequence of rotations and lifts and turns relatively large numbers could undergo arithmetic operations with great precision.  In the case of the Curta II, up to 15 significant digits of accuracy. There is a great video showing the operation of the Curta here. Or, see Jan Meyer's amazing Curta simulator here.

I purchased my Curta from a fellow that used it during the 60s for rally car races.  The navigator for the car had the responsibility to see that the driver "paced" the car as prescribed by the rally rules.  This required quick and reliable computation under some difficult circumstances. I don't think a slide rule would have quite made it in that type of situation.  They were also used in airplane navigation and in engineering and scientific computation.  They pretty much went out of favor at the same time as the slide rule during the 1970s.

I found my Curta many years ago, when hand held mechanical calculators were out of favor, yet before the collector craze for older mechanical computing devices had started.  I keep it in a display case in my living room right next to my Thatcher 4013 Calculator.  The reason I mention this is because I have a very interesting story about Edwin Thacher and his Cylindrical Calculator that I stumbled upon while searching for a Curta for my collection.  But that is going to have to be for another day. By the way, no, I didn't make a mistake on spelling the Thatcher/Thacher names above. Edwin spelled his name without a "t" (i.e. Thacher), but the engraver making the device for production misspelled his name on the engraving plate by putting in an extra "t".  The device was so precise and it would have cost so much to redo the engraving that they went into production with the wrong spelling for his name anyway, so the device is a "Thatcher".


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