Mechanical calculators: Olivetti Divisumma 24

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The Olivetti Divisumma 24 is a landmark calculator that is capable of performing the four arithmetic operations automatically. Its only electrical component is a motor, with a start capacitor. Multiplication and division are implemented mechanically, integrated to a back transfer mechanism. The machine also features a kind of memory mechanism as well.

I purchased this machine in February 2016 at an online auction site. The vendor warned in his ad that the machine was not working he did not know what was the problem, but from the photos I gathered its state was apparently good, with a depressed/stuck clear key, and the ad included an original-looking power cord. Its exterior appearance was good, the case was intact and all the keys were present. This machine weighs about 15 kilos, so shipping cost was about a third of what I paid for it.

Upon arrival, I managed to free the clear key, then I lubricated a little bit around, and risked powering it on to check on the motor. The motor hummed nicely, then I risked pressing the total key, and the machine did its thing. However, no calculations turned out right, and only a couple of the printer's columns actually worked. Once again, old lubrication seems to be the cause of the problem.

This machine has been manufactured in several places around the world, from 1956 to 1971. I found no reference to the actual date from the serial number so far. Since it's a Divisumma 24 GT, and from Argentina, my guess is that the manufacture date is closer to the end of the production, about 1970. The Argentinian model looks much better than the Italian one. The most common colors are a dark gray body with a black cap, whereas this one has an off-white body and a light gray top. Keys also follow the gray color scheme. According to information gathered online, the Divisumma 24 sold for about two-thirds of the price of a popular car (the Fiat 500), but its production cost was only ten percent of that. So its commercial success (the model may have reached a million units sold worldwide, six million for the entire D24 line) financed Olivetti for many years into the future. In Brazil, however, it does not seem that the Divisumma 24 was that popular, since very few of them are sold as antiques, as opposed to large numbers of machines such as the Summa Prima 20, Summa Quanta 20 and the FACITs.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

c1970 Olivetti Divisumma 24 s/n A14-3569

As purchased, in February 2016. Not bad on the outside, all-clear key depressed and machine locked up.

 As purchased

More about this machine

Operations manual (in German)

A blog entry describing the restoration of a Divisumma 24, including some nice drawings on the machine's modules and functions (in French)

Another Divisumma 24 from Argentina, with images and more info on the machine

A factory training movie from the production days showing one stage (the 22nd!) in the assembly of the Divisumma 24 (in Italian)

A video in which a Brazilian retired technician from Olivetti shows the operation of a very well preserved machine, step by step (in Portuguese)

An interview with Mr. Jay Respler, who worked for Olivetti-Underwood in the peak of mechanical calculators

Description of a restoration effort, with a nice partial-reassembly to present the way calculations work (in German)

A schematic summary of the Divisumma 24

John Wolfe's Web Museum, description of the entire Olivetti line along time

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divisumma24.txt ยท Last modified: 2016/03/25 19:05 by clodoveu
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