* Back to Mechanical Calculators

Olivetti's series of electromechanical calculators from the late 1950s includes the Elettrosumma 22, the Multisumma 22, the Multisumma 24, the Divisumma 24 and, later, the Tetractys 24. A later development of this line produced the Divisumma 26GT, with a much altered exterior design.

While the Elettrosumma 22 was basically an adder, the Multisumma 22 included semi-automatic multiplication. The Divisumma 24 was able to perform the four basic arithmetic operations, and the Tetractys had a double accumulator and functions that resemble special memories in later electronic machines. The Multisumma 24 was basically a reduced Divisumma 24. The entire line advertised on its speed, from 210 (Elettrosumma 22) to 235 cycles per minute (Divisumma 24 and Tetractys).

(Well, since one cycle means one turn of the motor, and with one cycle you perform a single addition or subtraction, one might say in current computer architecture terms that these machines have a clock frequency of 3.9 Hz. A common 2016 Intel Core i7 processor, running at 4.5 GHz, performs sums about a billion times faster, one per 0.2 nanosecond. Also to their disadvantage, 13-digit mechanical calculators operate with the equivalent of 22-bit integers, as opposed to the i7's 64 bits.)

The Olivetti Multisumma 22 is then an electromechanical calculator capable of assisted or semi-automatic multiplication (not only a repeated add function, which it also has), along with the usual adding and subtracting functions. Multiplications can be embedded within sums, so sums of two-factor products can be obtained with no re-entering of partial results.

The assisted multiplication is not very intuitive for people used to modern calculators. For instance, let's multiply 256 by 256. You enter “2566” in the keyboard; the extra 6 is the last digit of the multiplier. Press the big black “X”. The machine operates and prints “256” and the “6” of the multiplier is printed sideways, in the right side of the paper. Then you press “5” and “X”, to enter the second digit of the multiplier. The machine prints “5” sideways in the corner. Then you press “2” and simultaneously press “X” and the slim “*” right next to it, indicating that the multiplier is finished. Then the machine prints “2” sideways, advances, and prints the result in red, “65536 *”. Multiplications can be combined with sums and subtractions, since if the slim “*” key is not pressed, the subtotal remains available, so the input register can be cleared and subsequent operations can be accumulated.

The input register has 12 digits, and the results can be printed out with 13 places, plus four hand settable digits, used for optional identification of the calculation or dating. This machine also has the “label” function (”<” key) of most printing Olivettis.

At about 10 kilos, the Multisumma 22 weighs almost twice as much as the Multisumma 20, a more recent relative of the Summa Prima 20. My unit has the usual color scheme for this family of machines, green and black, unlike my Divisumma 24, from Argentina, which is white and light gray. It looks just like the Elettrosumma 22, which has no multiplication feature.

I purchased this machine in March 2017 at an online auction site. In Brazil, the Multisumma and the Elettrosumma are much rarer than the larger Divisumma 24. The vendor warned in a video that the motor was running, but the numerical keys were frozen. An original power cable was supplied. Its exterior appearance was good, the case was intact and all the keys were present. The back of the motor has a stamp with a date: May 29, 1962.

I disassembled a small part of the machine, including the paper handling mechanism, the ribbon mechanism and the motor assembly, so that inner parts of the mechanism could be reached for some cleaning using a jet of kerosene, applied with an airbrush and some air pressure. Then I approached each problem the machine had by identifying the parts of the mechanism that were involved in each faulty operation for further cleaning and adjustment. This took me from making it clear without locking up, then to adding subtracting with negative balance, and on to loosening all printer digits. Multiplication was the hardest, as a long piece was bent from being pressed against a locked part of the mechanism. Another small lever, embedded deep inside the machine, was also slightly bent, making it miss multiplication factor counts and produce wrong results; it took me five days to find the source of this problem.

There was also a problem with a capacitor-resistor circuit that works around the machine's main electrical switch. The circuit is supposed to avoid sparking in the switch, but the old oil capacitor leaked and shorted out, and had to be replaced. This old capacitor was manufactured by Ducati, a brand currently associated with motorcycles (see https://en.wikipedia.org/wiki/Ducati_Energia). Oil capacitors are rare nowadays, so I found a suitable polyester one, and now everything works very nicely – although noisily!

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

**c1962 Olivetti Multisumma 22 s/n M-203500 **

External views, after cleaning and revision.

A view of the motor, stamped with a production date: 29 May 1962. The yellow capacitor to the left is still the Ducati one.

Internal views, taken while and right after cleaning.

As purchased, in March 2017. Not bad on the outside, numeric keys inoperative, most functions locked.

Some of the innovative and artistic ads for the Olivetti Multisumma 22 and Elettrosumma 22.

I put together an operating manual for this machine, I hope it helps anyone interested in bringing a Multisumma 22 or an Elettrosumma 22 back to life.

**More about this machine**

A video showing the Multisumma 22 in operation

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