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Calculator Mechanisms

Common types of Mechanical Calculator Mechanisms:

1. Full-keyboard key-driven calculators
2. Full-keyboard "Add-lister" calculators
3. 10-key "Add-lister" calculators
4. Rotary pin-wheel calculators
5. Stepped gear calculators
6. "Troncet" type stylus calculators
7. Dial calculators

There are also other, less common, types of mechanical calculator.

1) 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.

Examples

• Comptometer.

Comptometer

2) 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.

Examples

• Burroughs add-lister.

Burroughs Add-lister

3) 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)

4) 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

5) 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)

6) "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)

7) 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)

Vintage Calculators

© Text & photographs copyright Nigel Tout   2000-2010 except where noted otherwise.