The "pin-wheel" from which these calculators take their name is a circular disc or wheel which has nine retractable pins extending radially around part of its circumference. The pins can be extended or retracted by a setting mechanism, which is generally operated by rotary levers. The pin-wheels and setting rings are assembled into a "rotor" or cylinder, which rotates forward or backward as the handle is turned. The extended pins act as gear teeth to advance a register by the corresponding number of places. The wheel in the illustration shows five pins extended on the left-hand side. (The two pins on the right are part of the tens-carry mechanism).
Although the notion of a variable-toothed gear was known to Leibnitz in the 1600s, it was not used in practice until the early 1870s, when the pin-wheel calculator was developed more or less simultaneously by Frank Baldwin in America and Willgodt Odhner, a Swede living in Russia.
Baldwin's machine was developed during 1872 and 73, and was sold and used commercially from 1874. It is generally acknowledged as the first practical pinwheel calculator, although it is often called the "Baldwin 1875" machine after the year in which it was granted its US Patent (No. 159244). The illustration (from the patent drawings) shows a cross-section of the machine, with the setting lever at the top and the pins extended at the lower right. The arrangement at the left-hand side is a printing mechanism to take an impression of the raised numerals on the register wheels. Baldwin was a prolific inventor who continued to develop many and varied calculator mechanisms (including that for the Monroe line) until his death at 87 in 1925.
Odhner's machine was developed in St. Petersburg from about 1874. This illustration from his US Patent (No. 209416) of 1878 shows a pinned disk and setting mechanism that is directly comparable to the modern version shown above. Odhner's design had the greater commercial success, and it was his name that became more generally associated with the pinwheel mechanism. By about 1890 (US Patent 514725) the Odhner calculator had developed into the form which was to endure more or less unchanged for the next eighty years. In 1892 the patent rights were sold to a firm in Germany, who developed a very successful line of machines under the name "Brunsviga". Similar machines soon appeared from many other manufacturers. After the Russian revolution in 1917, Odhner's heirs re-established the company in Goteborg, Sweden, under the brand name "Original-Odhner".
The pin-wheel calculator was a simple and reliable machine, which was capable of all four arithmetic functions. Addition and subtraction were performed directly, while multiplication and division were accomplished by simple procedures involving repeated additions (or subtractions) and carriage shifts.
Options and additions to the basic mechanism included:
Pin-wheel machines to Odhner's basic design were built (and copied, legally or otherwise) in many countries of the world. Those found in Australia were generally built in Europe or Japan. The machines were in continuous production for almost one hundred years, from their beginnings in the 1870s until overtaken by four-function electronic calculators in the 1970s.
Follow the links to separate pages describing a selection of pin-wheel calculators from Brunsviga, Original-Odhner, and Facit, or read on for an assortment of other brands.
Britannic Model 2A, S/N 8309
Digits: 9 rotor, 10 counter, 18 accumulator
Dimensions: Body 145W x 100D x 90H, overall width 310mm
Weight: 3.8 kg
Manufactured: London, England.
The Britannic Model 2A is a small and simple pinwheel calculator which was made in England by Guy's Calculating Machines of Wood Green, London. The body of the machine is built from three brass castings with sheet-metal top covers. Although the calculator itself is in very good condition, it is missing its original wooden base and cover.
The rotor pinwheels are 48mm in diameter, with the setting rings spaced on 6mm centres (ie, built to metric dimensions). A rotor clearing lever is provided on the face of the machine, to the left of the setting rings.
The carriage has an 18-digit accumulator, with tens-carry extending to 13 places. There is no tens-carry on the counter register. The carriage shift mechanism has a sliding bar which moves one place at a time in either direction, and a lever to allow continuous movement.
Walther Model RMKZ, S/N 21917
Digits: 10 rotor, 8 counter, 13 accumulator
Dimensions: Body 185W x 130D x 135H, overall width 300mm
Weight: 3.6 kg
Manufactured: Zella-Mehlis, Thuringia (Germany), 1924-1945
The Carl Walther company introduced a line of pinwheel calculators in 1924 to supplement their primary business in sporting firearms.
Model RMKZ is built from aluminium-alloy castings and is (relatively) light in weight. It has a setting check dial and tens-carry on the counter, but no back-transfer mechanism. The carriage is spring-loaded towards the left, and is moved one step at a time by the two vertical levers next to the winding handle. A button at the front releases the detent to allow continuous movement. The accumulator register has small fibre thumbwheels next to each numeral wheel to allow values to be entered directly, eg, in setting up a division.
The Walther factory in Zella-Mehlis was lost during the war, but calculator production resumed in 1948 at Niederstotzingen in West Germany. A new version of the Model RMKZ was the first post-war product, followed later by a range of ten-key printing calculators.
Schubert Model DRV, S/N 137791
Digits: 10 rotor, 8 counter, 13 accumulator
Dimensions: Body 210W x 140D x 135H, overall width 330mm
Weight: 5.6 kg
Manufactured: Rastatt, West Germany, 1950s
Emil Schubert (1883-1952) built the Thales pinwheel calculator in Rastatt in Germany from 1911. After WWII the factory was re-established in Rastatt to produce a new line of calculators under the "Schubert" name.
Model DRV is a colourful machine designed to facilitate one-handed operation. The rotor has ten setting rings on 7mm centres, with a check dial above and a quick-clearing lever to the right.
The carriage has separate clearing levers for each register. The right-hand lever normally clears both, but the coupling can be disconnected by pressing the small tab between the registers. The carriage shift levers at the front are replicated in the double-sided lever below the winding handle.
The counter register has full tens transfer, with automatic reversing and manual override. The carry mechanism is unusual, in that it uses a simple odometer-style register with a powered "helper" mechanism to assist each dial over its detent.
The machine has a back-transfer mechanism operated by the handle at the right-hand rear. The rotor clearing lever is pushed rearwards and held, then back-transfer lever is pulled forward and latches. The result is transferred as the accumulator is cleared.
Multo Model 3, S/N 8145
Digits: 10 rotor, 8 counter, 13 accumulator
Dimensions: Body 170W x 160D x 130H, overall width 310mm
Weight: 5.6 kg
Manufactured: Malmo, Sweden, around 1950
The Addo company of Malmo in Sweden produced a range of slide-set adding machines from 1920. These were replaced in 1927 by full-keyboard adding and listing machines. Ten-key machines were produced from 1936, and pin-wheel machines under the "Multo" brand from 1949. Addo/Multo was absorbed into the Advidaberg/Facit/Odhner group in 1966. The Addo name continued to appear on Odhner pinwheel machines until production ended around 1970.
The Multo range was designed specifically for single-handed operation, with all of the controls located on the right-hand side.
The Multo rotor has ten setting rings on 7mm centres, with a check dial above and a quick-clearing lever to the right. The carriage has only one clearing lever, which normally clears both registers. Pressing the adjacent tab disconnects the accumulator and clears only the counter (as in setting up a division). It is not possible to clear only the accumulator.
The carriage is spring-loaded to the left, and is moved stepwise in either direction by the lever under the winding handle. A button on the front of the machine releases the carriage and returns it fully to the left. There is no tens-carry on the counter, and no back-transfer mechanism.
This early machine carries only a serial number (3-8145), with no indication of a brand or manufacturer.
Multo Model 113, S/N 38540
Digits: 10 rotor, 8 counter, 13 accumulator
Dimensions: Body 170W x 160D x 130H, overall width 310mm
Weight: 5.9 kg
Manufactured: Malmo, Sweden, 1950s
Multo Model 113 is a full-featured version of the Model 3. It has a tens-carry mechanism with automatic reversing on the counter register, a back-transfer mechanism from the accumulator to the rotor, and an Addo/Multo badge at the top left.
The back-transfer is operated by pressing the button to the right of the setting rings when the rotor clearing lever is pulled forward. A small red indicator appears at the right of the carriage when the back-transfer is engaged, and a lever below the indicator allows the mechanism to be released if the button was pressed accidentally.
The carriage release button has been removed from the front of the machine and replaced with a rocking dome nut just inboard of the winding handle.
Felix calculator, S/N E55844
Digits: 9 rotor, 8 counter, 13 accumulator
Dimensions: Body 160W x 110D x 130H, overall width 330mm
Weight: 5.8 kg
Manufactured: Kursk, Russia
The "Felix" calculator is said to be named after Felix Dzerzhinsky, who established the Soviet calculator factory in Moscow in 1924, and later achieved fame as the founder of the KGB.
The machine illustrated has a cast-iron base and frame, with a sheet-metal carrying case. The mechanism and the internal construction are rather basic, but the machine is quite well-built and is still in good working order.
Felix calculator, Model M, S/N E215979
Digits: 9 rotor, 8 counter, 13 accumulator
Dimensions: Body 160W x 155D x 130H, overall width 320mm
Weight: 3.6 kg
Manufactured: Russia
A later version of the Felix, using light-alloy castings and weighting only 3.6kg.
Tiger Calculating Machine, S/N 18084
Digits: 9 rotor, 8 counter, 14 accumulator
Dimensions: Body 180W x 150D x 110H, overall width 290mm
Weight: 5.8 kg
Manufactured: Osaka, Japan, 1937
The Tiger Calculating Machine Co. Ltd. of Osaka was established in 1923, and became the largest of the Japanese mechanical calculator companies.
The machine illustrated dates from 1937. It is a conventional pinwheel machine, which is solidly built of cast iron and brass. The nine pinwheels are 49mm in diameter, with the setting levers spaced 6mm apart. A quick-clearing lever is located to the left of the setting levers.
The accumulator has 14 places, but the tens-carry only extends to 13. There is no tens-carry on the counter register. The carriage shift and clearing mechanisms are similar to the Trinks Brunsviga.
Tiger Calculating Machine, S/N 144060
Digits: 10 rotor, 10 counter, 20 accumulator
Dimensions: Body 235W x 165D x 130H, overall width 430mm
Weight: 5.8 kg
Manufactured: Osaka, Japan, 1957
This Tiger machine dates from 1957, although the case design is largely unchanged from the 1930s. The mechanism uses a modified pinwheel with a continuous ring gear instead of individual pins on the rotor, similar to that developed by Carl Friden at Marchant around 1920. The setting levers do not move as the rotor turns, but cause the ring gear to extend and retract at the appropriate times to advance the register by the required number of positions.
The Tiger calculator is very solidly built. The mechanism includes a setting check dial and quick-clearing lever, a wide carriage with a 20-digit accumulator, and a back-transfer mechanism operated by the small handle at the front left-hand corner of the baseplate.
Busicom Model HL-21, S/N 331499
Digits: 10 rotor, 11 counter, 21 accumulator
Dimensions: Body 205W x 165D x 135H, overall width 410mm
Weight: 5.0 kg
Manufactured: Japan, late 1960s
Busicom, or the Nippon Calculating Machine Corporation, were the people who commissioned Intel to make a chipset for an electronic calculator. That chipset became the Intel 4004, the world's first "microprocessor".
The Busicom HL-21 is a full-featured mechanical calculator with a setting check dial, back-transfer mechanism, and a 21-digit accumulator. The setting levers are only 5.5mm apart. The 11-digit counter register has full tens transmission, implemented using a miniature version of the pinwheel carry mechanism on the main rotor.
