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Mechanical Calculators

Principles of mechanical calculators

The basic operating principles of mechanical calculators changed little from the end of the 19th century to their obsolescence in the 1970s, though there were many developments in the mechanisms and the materials used. This site shows representative examples of the different types.

Models made before the end of the 19th century are very rare and are usually only to be seen in museums and pictured in books. These include the Pascaline invented by Blaise Pascal, and the Stepped Reckoner invented by Leibniz, both in the 17th century, and Charles Xavier Thomas's Arithmometer in the 19th century.

The mechanical calculators featured here are typical machines which were ousted by the cheap electronic calculators which were gradually developed during the 1960s and early 1970s.

Note that the larger mechanical machines were not intended as personal calculators but would have been used in company accounting departments, technical institutions, or similar. Also they did not appear for sale to the general public in stores but were generally sold to companies by representatives of the manufacturer or through a distributor.

Common types of Mechanical Calculator Mechanisms

Full-keyboard key-driven calculators

• Have a column of keys 1-9 for each decade. Not pressing a key in any column leaves 0 there.
• Add immediately a key is pressed.
• Basically only perform addition, though the other functions are possible using special techniques.
• Keys in different columns can be pressed simultaneously.
• A lever on the right clears the accumulator register.
• Abbreviated keyboards are possible with columns of keys 1-5 for each decade.

Comptometer

Full-keyboard "Add-lister" calculators

• Have a column of keys 1-9 for each decade. Not pressing a key in any column leaves 0 there.
• Keys pressed are latched. The number entered is printed on the listing paper and added to or subtracted from the accumulated total by pulling the lever.
• Basically only perform addition and subtraction, though the other functions are possible using special techniques.
• Totals and sub-totals can be printed.

Burroughs Add-lister

10-key "Add-lister" calculators

• Have only the one set of the 10 keys 0-9, like a modern calculator.
• The digits of numbers are entered sequentially, as on a modern calculator, and are latched internally. The number entered is printed on the listing paper and added to or subtracted from the accumulated total by pulling the lever.
• Basically only perform addition and subtraction, though the other functions are possible using special techniques. Advanced calculators may be able to perform multiplication and division automatically.
• Totals and sub-totals can be printed.

Examples

• Olivetti Summa Prima.
• Olivetti Electrosumma 22-R (driven by electric motor).
• SCM 1011 CB (driven by electric motor).

Olivetti Summa Prima (with Sterling currency keyboard)

Rotary pin-wheel calculators

• Numbers are entered by moving levers to the required digits (on calculators made by Facit a keyboard is used). This raises the same number of pins on each pin-wheel as the number set in that decade.
• Rotating the mechanism, either manually with a crank or by electric motor, adds the number entered to the accumulator (or subtracts the number from the accumulator if rotated in reverse).
• By rotating multiple times and shifting the accumulator very fast multiplication and division is possible.

Examples

• Odhner
• Muldivo DER.
• Facit C1-13.

Original Odhner

Close up from the right end showing the pin wheels with the number of pins raised on each wheel depending on the number set by each lever (from top to bottom 0087654321).
These pins act as gear teeth when the crank handle is turned.

Stepped gear calculators

• Have a column of keys 1-9 for each decade. Not pressing a key in any column leaves 0 there.
• Pressing a key shifts its associated stepped gear sideways so that the number of teeth engaged is the same as the number on the key.
• Rotating the mechanism, either manually with a crank or by electric motor, adds the number entered to the accumulator (or subtracts the number from the accumulator if rotated in reverse).
• By rotating multiple times and shifting the accumulator, very fast multiplication and division is possible.

Examples

• Madas.

Madas (driven by electric motor)

"Troncet" type stylus calculators

• Small, flat calculators, with vertical windows behind which sliding strips with holes and the numbers 1-9 can be seen.
• Numbers are entered by inserting the stylus in the hole against the required digit and sliding the strip to the end of its movement.
• Any carry must be performed manually.
• Usually have one scale for addition and one for subtraction.
• Basically just perform addtion and subtraction.

Examples

• Addiator.

Addiator (sterling currency version)

 Dial calculators

• Have simple gears marked with numbers for each decade.
• Placing a finger or stylus in each digit of a number in turn and moving the gear till it stops adds the number.
• Carry is performed automatically.
• Basically just perform addtion and, sometimes, subtraction.

Examples

• Bowler Countess.

Bowler Countess (Sterling currency version)

Odhner
Invented 1874: featured model 1935 - 1945
Rotary pinwheel calculator.

Comptometer
Invented 1884: featured machine is Model J, Sterling currency, 1926 - early 1940s
Full-keyboard key-driven calculator.

Addiator
Invented 1889: featured model 1920s - 1930s
"Troncet" type stylus pocket calculator.

The Millionaire
1889 - 1935
Direct multiplying machine.

Addometer
1900s - 1960s
Dial stylus calculator.

Golden Gem
1900s -
Chain adder.

S and N / The SUN
1910 -
Chain adder.

Monroe LN-160X
First model 1911: featured model 1950s - 1960s.
Stepped gear calculator with full keyboard.

Brunsviga 10
Mid 1930s.
Compact design of stepped gear calculator.

Curta I
1947 - 1970s
Hand-held stepped gear calculator.

Facit C1-13 and ESA-01
1950s - 1960s
Hand driven and electrically driven, keyboard-set, pinwheel calculators.

Marchant Figurematic
1950s - 1960s
Electrically driven, full-keyboard calculator with automatic, high-speed multiplication and division.

Plus Adder
1950s - 1960s
Minimalist abbreviated-keyboard key-driven calculator.

Madas
1950s - 1960s
Electrically driven, full-keyboard stepped-gear calculator with automatic multiplication and division.

Burroughs Add-lister
1960s
Full-keyboard add-lister.

Wheel Adding Machines - Resulta, Countess, addipresto
1950s-early1970s
Wheel adding and subtracting machines.

Olivetti Elettrosumma 22 and similar models
1950s
Electrically driven 10-key add-lister.

Muldivo Mentor / Walther WSR-160
1960s
Rotary pinwheel calculator, with improved setting mechanism.

Nippon Calculator / Busicom HL-21
1960s
Rotary pinwheel calculator.

Smith-Corona-Marchant 1011 SB
1960s
Electrically driven, 10-key add-lister.

Sumlock Comptometer 993s
1964
A very late Comptometer design, electrically driven, with memory register.

Kingson Four-Rule and Faber-Castell combined Addiator and Slide-rule models
1960s - early 1970s

A combined "Addiator" and Slide-Rule.

Imperial Office Master
1970
A very late mechanical 10-key add-lister.

Addiator Addfeet Junior
to 1980s
Feet and Inches Addiator.

This is only a small sample of mechanical calculators. There were many more models from many manufacturers.

For more featured non-decimal machines see the Non-decimal Calculators section.

For featured British mechanical calculators see the associated British Vintage Calculators site.