| Production year: |
1956 - 1971 (This machine is an early type, with a brush motor and black minus key. Later versions have a capacitor aided motor and an orange minus key)
Andrea Celli: "The MC-24 series (Divisumma basic/GT/CR and Tetractys) was the most popular and successful Olivetti machine. Circa 1.500.000 machines sold (In internet you can find also crazy data like 4 or 7 millions). By sure 1-million machine were produced in 1967. MC-24 series were produced until 1973. Then 1.5 million is an affordable estimate.
Another curious issue is the rate making/selling price. Beltrami, Olivetti CEO, reported that in 1971 making cost was 30-35.000 Lire whilst the machine was sold for 300.000 Lire!
A rate 1/10 is quite unusual. I suppose this is due to Capellaro's genial project. He reduced all frictions and stress to minimum. This allowed Olivetti to use cheap materials instead of special steel. The machine includes just a couple of (expansive) bearing rolls. Nevertheless the machine was strong and affordable. An old hardware shop near my institute is still using a Divisumma-24" |
| Machine story: |
2014-05-15
Internally the machine was partly rusted, especially on those area's where the printing unit has open connection to the internal metal pieces. The most urgent parts removed and separated cleaned; the electric motor and rubbers removed and the whole machine sprayed with penetrating oil. Two days rest.
2014-05-17
Repeatedly moving the pin block (key) gives a smooth handling of the pressed numerical key's again. Manual turned the main axis the adding works after all the digits manually pushed at the printer heads. Some parts extra push was needed. It was first manual not possible to operate the total sum. A few turns on the worm wheel made this possible. This is not defect, it has mechanical reasons. Multiply was operating.
The results of all the calculations are not printed yet.
2014-05-18
Adding and subtracting works as long as no carry is involved. Automatic multiply gives a strange result (please see the result picture). Needs extra examination on the carry mechanism.
2014-05-26
Try to figure out how I can reach the carry mechanism, to see how it works and what might be the reason for not producing the carry? From the front it was not possible without demounting to much and what is without special tools not mounted again.
From the back I have demount the rubber printing role and the mechanism surrounding that. Even then I had not a good few to analyze the mechanism responsible for the carry.
But it was nice observe the rocker switch, the mechanism to put the opposite gear to the tooth racks, at a subtracting.
In front / the first tooth rack, seen from the back, is the memory / register to store the multiplicand.
I have stopped the search so far. It was until now not possible to analyze the mall function. Try to get more information first, if it is possible to demount the necessary parts, and which one are those, before further examination.
2014-06-02
An other nice looking but completely blocked machine on several places, a not functioning keyboard unit and as well on the carry,
I have removed among more, the carry and register parts. (By the way: The motor unit, which was of the capacitor run type and the main axis are used as example at the electric drive chapter.)
The dismantled carry unit showed, that the carry plates are mounted as a daisy chain and are fixed to each other and on the axis where they mounted on. So now sprayed that unit several times and let the penetration oil do their work on the separate unit and the complete machine. On the demounted it did not work, but fortunately on this (complete) machine it did!!!!
After a few day's penetrating oil let do his work a few digits start to generate carries. After testing 999999999999+1 several times, all digits generate carries consistently. Multiplication and divide test passed now as well several times in a row.
Interestingly on a few parts of the dismantled machine, where it was blocked and others on fixed screws with cylindrical shafts etc, I noticed white dry surfaces. It looks like aluminium oxide.
Never noticed that earlier on calculators before!
The good thing is the case and a few other parts (the add front key, the print unit), that comes from the called other machine.
I add a picture of both machines the Tetractis and the Divisumma 24 side by side.
2014-06-04
On the listing I noticed a small c (normally for minus or negative balance) after the divide result, but as result of positive numbers not logical. |