Mechanical Calculators

Calculators are specialized computational devices, optimized to perform arithmetical functions, most often under the direct control of a human operator. The earliest digital calculators were completely mechanical, utilizing thousands of moving metal parts to perform addition and subtraction, and in more advanced designs, multiplication and division as well.

Complex mechanical calculation can be traced back to Wilhelm Leibniz's stepped reckoner, completed in 1694. The stepped reckoner was capable of performing all four arithmetical operations, but was limited in reliability due to the relatively poor machine tolerances of the time. Leibniz's stepped cylinder mechanism would be adopted by many later machines, including the Curta mechanical hand calculator.

Charles Babbage started contemplating mechanical calculator designs in 1812. Ten years later, Babbage began work on his Difference Engine, a gigantic mechanical calculator designed to compute values of polynomial functions. Babbage never completed the Difference Engine, despite receiving project funding from the British government for over a decade. Babbage later designed the Analytical Engine, a programmable calculator which used Jacquard punched cards to store program data. While the Difference Engine was partially built, the Analytical Engine was a wholly unrealized design. Nonetheless, the Analytical Engine stands as the earliest prototype of modern computation.

Beginning in the mid-1800s, improved machine fabrication technology and a surging demand for machine-assisted calculation prompted dozens of companies to jump into the desktop mechanical calculator market. The first successful design was the Arithmometer, first manufactured in 1851 from a design conceived by Thomas de Colmar three decades earlier. Many 20th century data processing behemoths, such as IBM, Burroughs and NCR can trace their roots to the mechanical calculation industry of the late 1800s. IBM produced punched card-driven tabulation machines for the US Census, Burroughs was dominant in desktop adding machines, and NCR commanded most of the retail cash register market. Dozens of other smaller companies competed with Burroughs for the desktop adding machine market, with both Comptometer-style and ten-key designs. The latest mechanical calculators were motor-driven, but otherwise similar to the earlier hand-cranked models.

Bohn Contex 10
 
Bohn Contex 10


The Bohn Contex 10 is a portable 10-key mechanical calculator, manufactured by Brdr. Carlsen A/S in Birkerod, Denmark. When a number is entered on the keypad of the Contex 10, a pusher extends one of a series of pins from the front of the keypad assembly. A row of sensing levers is positioned in front of the pins. When the adding bar is depressed, the sensing levers pivot downward across the pins, stopping when they contact an extended pin. The opposite ends of each lever have a toothed face, which meshes with the result register.

The Contex 10 was a widely adopted adding machine. As of 1962, Bohn was advertising the $125.00 Contex 10 as a "portable computer", emphasizing its small size and weight, and its suitability for use while traveling. Bohn also offered a motorized Contex for $235.00.

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Burroughs Visible Adding Machine, Class 3
 
Burroughs Visible Adding Machine, Class 3


Originally known as the Burroughs Pike Machine, the Class 3 is the earliest of Burroughs' low profile calculators, foregoing the tall glass-sided construction of previous models in favor of a much flatter design which can be operated upon a normal desktop. Another key feature of the Class 3 is that the printed results are visible to the operator, instead of being out of view on the back of the machine.

The Class 3 mechanism was designed by William H. Pike of the Pike Adding Machine Company. Burroughs acquired Pike in 1909, and the Class 3 was introduced that same year, although volume production did not begin until 1911. The Class 3 was a popular adding machine, with numerous functional and cosmetic variants. The example pictured here is a seven-column variant, serial number 229362, manufactured around 1916.

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Lanston Monotype 'The Barrett'
 
Lanston Monotype 'The Barrett'


Glenn J. Barrett was a pioneering engineer of typewriters and mechanical calculators, and produced a number of designs for Burroughs, L.C. Smith (later Smith & Corona) and Remington. In 1910, Barrett designed a new type of calculating mechanism, and later launched the Barrett Adding Machine Co. in 1914. In 1922, Barrett sold his company to Lanston Monotype, which continued to manufacture Barrett calculators into the 1940s.

The model pictured here was produced during the Lanston Monotype era, and was marketed simply as 'The Barrett'. The Barrett is equipped with a nine-column keyboard, 12-digit accumulator and printer.

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Monroe 'MonroMatic' CSA-10
 
Monroe 'MonroMatic' CSA-10


Prior to the introduction of electronic calculators, the Monroe 'MonroMatic' CSA-10 was among the most powerful desktop computation devices ever built. The operation of the CSA-10 is derived from Gottfried Leibniz's original stepped drum mechanism, and is capable of performing fully automatic multiplication and division. Unlike its primary competitor, the Friden STW-10, multiplicands are entered on the main Comptometer-style keypad, rather than being entered on a separate ten-key keypad.

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Olivetti Underwood Electrosumma 22
 
Olivetti Underwood Electrosumma 22


Introduced in the mid-1950s, The Olivetti Electrosumma 22 is a large desktop adding machine with 12-digit input and a 13-digit readout. The heavy duty print mechanism has four user-settable print wheels to the left of the result field, and can accept paper up to 100mm wide. Olivetti also manufactured another version of the Electrosumma 22, designed to accomodate British currency, with five additional entry keys above the numeric keypad.

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Remington Six-Column Adding Machine (Unknown P/N)
 
Remington Six-Column Adding Machine (Unknown P/N)


This calculator, manufactured by Remington, is a fairly typical example of a 1960s home or small business adding machine. It features a six-column full keyboard, and a seven-digit mantissa. This machine has no dedicated mechanical display; readout is provided by an impact printer. Although motorized adding machines were readily available at the time, this machine is entirely mechanical. A lever on the side of the machine is used to perform addition and subtraction, and to erase the contents of the accumulator.

Two other variants of this machine are currently known: a six-column variant with a full keyboard, and a variant with 10-key input. Rebranded versions of these machines were also sold by Sears.

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Underwood Olivetti Summa Quanta 20
 
Underwood Olivetti Summa Quanta 20


Introduced in 1961, the Olivetti Summa Quanta 20 is a compact, motorized adding machine, designed for home and small business accounting tasks. The Summa Quanta 20 is directly derived from the iconic Summa 15 and Summa Prima 20 manual adding machines, famous for their four-way function joystick which selects between add, subtract, total and sub-total. The motorized Summa Quanta 20 replaces the joystick with a two-way toggle switch for total and subtotal, while add and subtract have been moved to the keypad. All Olivetti machines of this type were designed by engineer Claus Capellaro and industrial designer Marcello Nizzoli.

As with many other office machines, Underwood secured US distribution and marketing rights for the the Summa Quanta 20. While most of these Olivetti-manufactured machines are branded Olivetti Underwood, the machine pictured here is branded Underwood Olivetti.

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Underwood Sundstrand 10140P
 
Underwood Sundstrand 10140P


The Undersood Sundstrand 10140P is one of many similar variants of the original ten-key adding machine invented by David Sundstrand in 1911. The Sundstrand adding machine is noteworthy as the first calculator to use a conventional ten-key entry method. Prior to the Sundstrand, all contemporary adding machines used a Comptometer-style full keyboard, with a nine-key column for each digit. A full keyboard is much faster for entry, as an entire number of any digit length can be entered in a single two-handed stroke. The ten-key keypad is much more user-friendly however, as it can be operated with a single hand, and does not require special training to use effectively.

In 1927, Sundstrand sold marketing and distribution rights of their machines to Underwood-Elliot Fisher Co, a leading typewriter manufacturer. Machines manufactured from 1927 onward bear the Underwood Sundstrand label. Oscar Sundstrand, David's brother and co-founder of the Sundstrand Machine Tool Co., joined Underwood after David's death in 1930, and continued to develop the Sundstrand adding machine until 1949.

The 10140P is a later motorized variant, with correction and repeat addition functions.

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Victor Comptometer 600 Series
 
Victor Comptometer 600 Series


Devices included in this entry:

Victor Comptometer 600 Series six column adding machine (Bakelite housing; pictured in thumbnail)
Victor Comptometer 600 Series eight column adding machine (metal housing)


The Victor Comptometer 600 Series was designed by Thomas O. Mehan, a veteran engineer of calculating mechanisms who built his first adding machine, the Brennan, in the 1920s. The ten-key Brennan design was later sold to Remington, who re-branded it as the Remington Monarch. Mehan was hired by Victor in 1938 to head up their R&D department, and introduced the 600 Series mechanism in 1939. The 600 Series and its numerous minor variants would live on until the 1970s, becoming one of the most popular adding machines ever built.

Mehan also developed the 700 Series, a line of ten-key machines which used the same internal mechanism as the 600 Series.

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