Jaap's Mechanical Calculators Page


Rheinmetall D II a

The Rheinmetall D II a
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The Rheinmetall D II a

The Rheinmetall calculator looks like it has a fairly standard design similar to the many other stepped drum calculators such as the Unitas/TIM or Archimedes. This version has an 8-column keyboard with input register display, and a carriage containing an 8-digit counter and 16-digit register.

It has some nice unique features. The carriage can slide right or left without needing to be lifted up. It can be shifted by turning the large knob at the front-left of the machine, not unlike the Monroe calculator. There is no separate lever for selecting whether the counter is incremented or decremented. The counter is always incremented when you turn the crank. You can however make a correction by turning the crank while holding down the C button, which undoes the previous addition or subtraction.

This particular model has automatic division. After setting up the division, you merely have to turn the crank repeatedly and everything happens automatically. When the register underflows during the division the next turn of the crank engages the correction button, the turn after that undoes the last subtraction, the next turn shifts the carriage to the left, and then the long division continues at the next position.

Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a

The mechanism uses stepped drums. To allow the digits to be fairly close together, each stepped drum is shared by two adjacent digits. There is a differential that can either transfer the motion of the crank to the calculation mechanism, or to the mechanism that controls the other aspects of automatic division such as the carriage shift.

It has serial number 7,843, which can be found in several places on the machine. The Rheinmetall machines were numbered consecutively, and this number dates my machine to about 1931. Later versions replaced the two selection levers with buttons.

Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a
Rheinmetall D II a

Rheinmetall video

Here is a video where I demonstrate my Rheinmetall.


Rheinmetall has a long and complicated history. The company "Rheinische Metallwaaren- und Maschinenfabrik Actiengesellschaft" was founded in Düsseldorf on April 13, 1889 by Heinrich Ehrhardt. He had a state contract to make ammunition, but the company also made other metal products, such as pipes, using a patented process that was also symbolised by the company logo. In 1901 they acquired an arms manufacturing plant in Sömmerda. This had been founded in 1827 by Nikolaus von Dreyse, and was where Dreyse pistols and guns were made, and after the takeover Rheinmetall continued developing and making them. They were one of Germany's largest arms manufacturers through the first world war.

After the war the manufacture of arms was no longer possible. The Sommerda plant used its precision engineering expertise to specialise in office equipment such as typewriters, bookkeeping machines, and calculators, while the larger Düsseldorf plant made larger steel items such as agricultural equipment. Richard Berk, who had worked at Ludwig Spitz was hired to design calculators. The first machines were made in 1922, but in the first four years calculator production remained very low with only about 600 machines made.

In 1926 Berk was let go, and August Kottmann replaced him. Kottmann had risen through the ranks, and had designed a way for the calculators to do automatic division and be driven by electric motor, and was now able to implement that design. The hand-driven calculators also were given the automatic division mechanism. In 1930 their first fully automatic calculators "Superautomat" were released. Versions of these machines were in production until the 1960s. Adding-listing machines were also released in 1933, and Kottman also designed a very successful invoicing machine, a combination of a typewriter and calculator, released in 1932.

In 1933 Rheinmetall acquired August Borsig Maschinenbau AG, a large manufacturer of locomotives and in 1936 when the merger was fully completed the name changed to Rheinmetall-Borsig. The headquarters was moved from Düsseldorf to Berlin, and by now the company was also making arms again for the German Ministry of War. During the second world war the company was nationalised and fully occupied with making weapons, ammunition and other military equipment, and very few office machines were produced. The large factories in Berlin and Düsseldorf were heavily bombed, but the smaller Sommerda plant survived relatively intact.

After the war and the division of Germany, Rheinmetall split apart. The Sömmerda plant fell under Soviet occupation, and was soon ordered to return to office machine production. Curt Herzstark worked there for about a year to finalise the development of his Curta design, but decided to flee the Soviet regime and go to Liechtenstein to put his machine into production. In what became West Germany the Rheinmetall plants in Berlin and Düsseldorf were rebuilt, but obviously were not allowed to make arms. The fact that there were essentially two independent companies with the same name and logo became problematic, because the Sömmerda calculators and adding machines were exported to the West through Berlin, and competed with Rheinmetall Düsseldorf, which also made some adding machines in the late 1950s.

In Sömmerda the calculators continued to be developed, especially because of the Western export market. In the early 1960s they began developing electronic invoicing machines, and eventually fully transitioned into electronics. Rheinmetall in West Germany returned to manufacturing arms, and today is a well known for making various armoured vehicles, gun turrets and tank guns, though they also have an automotive division that makes car parts.


The first hand-driven machines came with various keyboard and register sizes. They were given model numbers I or II, depending on register size, followed by a letter denoting the keyboard input size.

ModelInp × Cntr × Reg
Ib 6 × 6 × 12
Id 7 × 6 × 12
Ie 8 × 6 × 12
If 9 × 6 × 12
II 7 × 6 × 13
IIa8 × 8 × 16
IIc9 × 8 × 17

When variants and other types of calculator were made, the size designation was prefixed by one or more letters. When automatic division was introduced, the letter D was added, and later the simpler calculators without automatic division were given the letter K. Electrically driven ones got the letters ED (they had automatic division) or ER (with multiplier keys). The fully automatic machines (with automatic multiplication) were named Super Automat and were given the model letters SA. Further letters were used to denote additional properties or functions of the machine.

Base modelExtra functions
- Manual calculator
D Manual calculator with division
K Small (non-automatic) calculator
SAFully Automatic
AHManual Adding-Listing Machine
AEElectric Adding-Listing Machine
EElectric drive
WElectric carriage
LElectric clearing
SExtra register (Storage/Totaliser)
KConstant multiplier (model SAR)

The model letters are a little confusing, as the dividing line between what counts as a base model and what is extra functionality is vague. Not every letter combination is valid, so I have made a table of all calculator models for which I have found online evidence for in photos, ads or brochures.

Ib -, D-, KE-, KEW-, KEL-, KES-, KEWS-, -R, D-R, KE-R, KEW-R, KEL-R
Id -, D-, KE-, KEW-, KEL-, KES-, KEWS-, -R, D-R, KE-R, KEW-R, KEL-R
Ie -, D-, KE-, KEW-, KEL-, KES-, KEWS-, -R, D-R, KE-R, KEW-R, KEL-R
If -, D-, KE-, KEW-, KEL-, KES-, KEWS-, -R, D-R, KE-R, KEW-R, KEL-R
IIa-, D-, ER-
Adding machinesAH, AE, AHS, AES, AHW, AESW, AESM, AESWM


Anweisung zum Gebrauch der Rheinmetall Rechenmaschinen     (PDF, 28.9 MB or archive.org)
No. 675
100 page book
148mm × 209mm × 5mm

This is the German instruction book for all the Rheinmetall calculator models that were available in the late 1930s, namely the manual models with or without automatic division, and the electrically driven models KE, KEW, KES, KEWS, EDWL, SAL, and SASL. The last pages show the other products that the Sömmerda factory produced, such as typewriters, and adding machines.

Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual
Rheinmetall manual

Advertisements and articles

Below are some of the advertisements that I have found by Rheinmetall, not only for calculators.

1922-01-08 Helios
1923-08 Typewriter Topics
1924 14 Die Wasserwirtschaft
1924 15 Die Wasserwirtschaft
1925 Ernst Martin 2
1931-11-21 Algemeen Handelsblad
1936-08 Helios
1958-12-16 Western Mail
1974-03-08 Newcastle Evening Chronicle

Ernst Martin's 1925 book Die Rechenmachinen has an entry for Rheinmetall, but this was before the automatic division was introduced.

1925 Ernst Martin 1

The 1930 book Organisations-Lexikon by Walter le Coutre and Walter Thoms has an entry for Rheinmetall, which includes the models D, ED, and AER.

1930 Organisations-Lexikon - Rheinmetall

The newspaper articles that mention Rheinmetall are all about its role as arms manufacturer before and during the second world war.

1923-11-28 Yorkshire Post and Leeds Intelligencer
1931-10-15 Nieuwe Tilburgsche Courant
1934-11-19 The Scotsman
1942-08-03  Daily Record
1942-08-10 Belfast News-Letter


Here is a selection of the many calculator patents. I have excluded patents for adding machines and bookkeeping machines.

PatentFiling datePriority dateNameDescription
DE 319,63006-04-191912-03-1920Richard BerkStepped drum shared by two columns.
DE 319,63106-04-191913-03-1920Richard BerkSliding Carriage without lifting.
See also: US 1,641,615
DE 414,31423-08-192104-06-1925Richard BerkAddition/subtraction selector.
DE 419,31525-12-192424-09-1925Firma Rheinische Metallwaaren- und Maschinenfabrik SömmerdaInput clearing mechanism.
See also: US 1,599,093
DE 423,35117-07-192109-01-1926Firma Rheinische Metallwaaren- und Maschinenfabrik SömmerdaCounter mechanism.
DE 430,01411-10-192509-06-1926Firma Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAddition/subtraction selector.
See also: AT 94,575 B, US 1,637,827
DE 441,57131-12-192405-03-1927Rheinische Metallwaaren- und Maschinenfabrik SömmerdaSubtotals printing.
DE 443,58911-12-192505-15-1927Rheinische Metallwaaren- und Maschinenfabrik SömmerdaGrouped stepped drums.
See also: US 1,786,164, US 1,791,675
DE 447,94926-02-192604-08-1927Rheinische Metallwaaren- und Maschinenfabrik SömmerdaClearing interlock.
See also: US 1,797,699
DE 448,46224-06-192305-03-1928Richard BerkCarry mechanism
DE 449,79614-01-192621-09-1927Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAddition/subtraction selector with correction button.
DE 455,21721-03-192630-01-1928Rheinische Metallwaaren- und Maschinenfabrik SömmerdaStepped drums.
DE 457,86819-11-192626-03-1928Konrad Eichenauer; Rheinische Metallwaaren- und Maschinenfabrik SömmerdaElectric keyboard.
See also: CA 292,403, GB 280,891, US 1,773,392, US 1,808,213
DE 460,72031-08-192608-06-1928Rheinische Metallwaaren- und Maschinenfabrik SömmerdaElectrically driven calculator.
DE 499,25923-11-192805-06-1930Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic division.
See also: US 1,846,207
DE 505,13114-08-192715-08-1930Rheinische Metallwaaren- und Maschinenfabrik SömmerdaCalculator with electric output.
See also: CA 308,739, US 1,858,807
DE 509,74531-05-192913-08-1930Rheinische Metallwaaren- und Maschinenfabrik SömmerdaStorage register.
See also: CH 147,845, US 1,921,529
DE 519,10329-11-192703-03-1931Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic multiplication.
DE 530,00221-01-193020-07-1931Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic multiplication.
DE 544,64316-07-193024-02-1932Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic multiplication.
DE 546,45718-09-193014-03-1932Rheinische Metallwaaren- und Maschinenfabrik SömmerdaSuper Automat.
DE 554,27830-07-193007-07-1932Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic clearing.
See also: US 2,034,724
DE 565,19417-11-193126-11-1932Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic clearing.
CH 158,57229-07-193101-02-1933Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic carriage return.
See also: SE 76,885
DE 571,75505-11-193008-03-1933Rheinische Metallwaaren- und Maschinenfabrik SömmerdaCalculator with multiplication and storage.
See also: SE 75,976, US 2,035,322
DE 580,02705-11-193011-07-1933Rheinische Metallwaaren- und Maschinenfabrik SömmerdaSuper Automat.
DE 586,91908-07-193127-11-1933Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic clearing.
DE 590,13725-08-193129-12-1933Rheinische Metallwaaren- und Maschinenfabrik SömmerdaCarriage return.
DE 593,74515-02-193105-03-1934Rheinische Metallwaaren- und Maschinenfabrik SömmerdaAutomatic rounding.
See also: US 1,908,986, US 1,950,183
US 1,974,49404-08-193225-09-1934August Kottmann; Rheinische Metallwaaren- und Maschinenfabrik SömmerdaCarriage movement during multiplication.
CH 188,65422-05-193601-04-1937Rheinmetall-Borsig AktiengesellschaftElectric calculator with automatic division.
See also: US 2,227,785
CH 213,08107-02-194016-04-1941Maschinen- & Metallwaren-HandelsgesellschaftElectric backtransfer.


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