The Demos II
How to use the Demos II
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The Demos II is a calculator that uses a toothed segment mechanism, which is a simpler, cheaper alternative to the pinwheel mechanism. It has a 9-digit input register, using input pins much like a pinwheel calculator. While most pinwheel machines have the register and counter on a carriage that can move the input stays still, on the Demos the input is on the moving carriage. This carriage is inside the outer case so that it does not expose any of the mechanism. The 14-digit main register is above and behind the input carriage, and the 8-digit counter below and in front of the input.
My machine is in pretty good condition, and has serial number 1891-2. It was made in Switzerland in around 1923-1924.
The mechanism is much simpler than a pinwheel machine. Each input pin is part of a wheel with a toothed segment. When the crank is turned, all the input wheels rotate about one third of a revolution downwards and then back up again. During the down stroke, the main register moves forward to engage with the toothed segments, so each number wheel moves according to how much of the toothed segment was shifted by the input pin. The main register then moves away, and the carries are performed while the input wheels return to their original position.
While the Demos seems somewhat similar to a standard pinwheel machine, there is one big difference. The register only allows addition, so subtraction is done through the use of complementary numbers. The crank is turned clockwise for both addition and subtraction.
This is exactly as you would expect. Simply set the input pins to the number you want to add. The entered number is displayed in white digits in the row if holes in the middle of the input area. Turn the crank clockwise to add the input to the main register.
There is a knob on the left of the machine. To shift the carriage by one place,
simply pull the knob to the left (or push it right) until it stops. The carriage
will have shifted by almost one digit, and the next turn of the crank will align
the carriage properly. If you don't want to turn the crank at this position and
want to move one more place, you can turn the knob momentarily to remove the
current stop and the pull/push the knob again until the carriage stops at the
next digit. To move the carriage any amount in one go, turn the knob and keep
it turned while you pull or push it, and then the carriage moves without any
The input clearing bar has a pointer that indicates which digit in the counter will be affected by turning the crank given the current location of the carriage.
Multiplication is now as you would expect. Clear the counter. In the counter you will build the multiplier, the number you want to multiply the input with. This can be done left to right, right to left, or any other order. Shift the carriage so that the input bar indicates a digit in the counter that you want to change, and then turn the crank to increment that digit. When the counter displays the multiplier you want, the product of that number and the input will have been added to the main register.
Note that shortcut multiplications are not possible on this machine. The counter does not have a carry mechanism, and subtractions cannot be done by turning the crank in the opposite direction.
Subtraction is done by the addition of the complementary number. There are two displays of the current setting of the input pins - in the centre there is a row of windows displaying white digits, and a bit further up there is a row of windows displaying the complementary number in red digits. The white number and the red number together add to 1,000,000,000. This means that if you set the input to so that the red number has value R and turn the crank, it actually adds the the white number which is 1,000,000,000-R, so your value R gets subtracted, but there is a side effect of adding 1 in the tenth digit from the right, which you should just ignore.
Most of the input pins have ten positions, from 0 to 9 (or 9 to 0 in the red digits), but the right-most input pin has eleven positions, from 0 to 10 (or 10 to 0 in the red digits).
Given how subtraction works, the method for division follows naturally using long division. The value in the register will be divided by the (red )value in the input, and the result of the division will be stored in the counter. Shift the carriage to the left until the red non-zero digits lie just below the left-most digits non-zero digits in the register. Turn the crank clockwise, until the register underflows. Undo the last turn of the crank by turning it once anti-clockwise. This undoes the changes made by the last subtraction, making the remainder in the register positive again. Shift the carriage one step to the right if possible, and repeat. When the carriage cannot be moved any further then the division ends. The counter shows the result, and the register shows the remainder. Note that the leftmost digits of the register will contain some nonsense values due to the subtractions adding extraneous ones in those places.
Note that you can turn the crank anti-clockwise once to undo the last subtraction/addition, but not more than once. It simply subtracts from each digit in the register the corresponding input digit and any carry it has received. This undo operation does not involve performing carries from one digit to the next, but just sets each digit separately to its previous value.
Here is a video where I demonstrate my Demos II.
The company Moesch & Huber was founded by Carl Moesch and Hans Huber in Zürich. In 1921 Hans Huber created a calculator called the Uto. This was the predecessor to the Demos, and it seems to have essentially the same mechanism. It is not clear if any of these are still in existence. It was changed to the Demos in 1922 or 1923, which had a case of which the upper part was made from a single piece of cast aluminium, whereas the Uto's case consisted of metal plates that were screwed together. The Demos was improved to become the Demos II and then the Demos No. 3. Outwardly the three generations of Demos look the same apart from the markings, and I do not know what the mechanical differences are between them. It is possible that the ability to undo a crank turn as used in division was something introduced with the Demos II.
Here is a table listing the models. The exact years of production are guesswork.
|Model||Years||Known serial Numbers||Remarks|
|Uto||1921-1922||?||Unknown if any survive. Maybe they were converted to Demos. Case made from metal plates.|
|Demos||1922-1923||?||Case made from cast aluminium. Decal with Demos in cursive writing on the left, later Demos decal in gold on green.|
|Demos II||1923-1924||1891-2||Case has raised Demos II in top-right corner, and the gold-green Demos decal.|
|Demos No. 3||1925-1926||4125-2, 4239-2, 4379-2, 4524-2, 4946-2||Case still has raised Demos II, but also extra decal with No. 3 below gold-green decal.|
The Demos was not very successful, and in the second half of the 1920s Moesch & Huber switched to developing and producing the Direct calculator, which was soon improved to the Direct II. This was a full-keyboard calculator that became a lot more successful. In 1926 the Hannovera company in Germany started making a calculator that operated on exactly the same principle as the Demos, the Hannovera C and CK. It is not clear whether Huber licensed his Demos patents to them.
The company name shown on the Demos (and Direct) calculators is Theo Muggli AG, also based in Zürich. This company sold office equipment, mainly typewriters and calculators. It is unclear to me how much Theo Muggli himself was involved in the design and manufacturing of the Demos machines, but his company was the main distributor of them. Theo Muggli died in 1933, but the company that was named after him continued long after his death using the same name until it was finally dissolved in 1995.
Here are a few articles about the Demos and Theo Muggli that I found in online archives.
Articles about Theo Muggli
(The Royal Standard, Royal Typewriter Company Inc., 1922-1924)
(Tribune de Lausanne, 1923-09-14)
(The American Digest Of Business Machines, James H. McCarthy, 1924)
(Die Rechenmaschinen, Ernst Martin, 1925)
(Moderne Buero-Maschinen, 1931)
(Die Tat, 1941-04-24)
Here are the few advertisements for the Demos that I found.
Here are some advertisements by Theo Muggli, but they are mostly for typewriters and do not mention the Demos.
Here are all the patents by Hans Huber and Carl Moesch that I was able to find. Only one seems to be for the Demos adding machine.
|Patent||Filing date||Priority date||Name||Description|
|GB 1913/16,146||12-07-1913||11-06-1914||Hans Huber||Carry mechanism|
|CH 101,848||05-09-1922||16-10-1923||Hans Huber||Uto/Demos calculator|
See also DE 405,510 B.
|CH 122,102||25-03-1925||01-09-1927||Hans Huber||Direct display register|
See also AT 108,510 B.
|FR 613,220||22-03-1926||12-11-1926||Hans Huber||Carry mechanism, unknown listing machine|
|CH 234,614||10-09-1942||15-10-1944||Carl Moesch||Multiplication counter for a Comptometer type adding machine.|
Rechnerlexikon has pages for the
Demos II, the
Moesch und Huber company,
various Demos material, and the
Rechenmaschinen-Illustrated has a little info about the Demos.
Cris Vande Velde's collection of calculators includes a Demos No. 3.
Freddy Haeghens's collection includes a Demos II
Rechnen Ohne Strom shows a Demos No. 3
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