Plus & Sumlock
Mechanical Calculators


All of the mechanical calculators manufactured by Bell Punch were key-driven machines of the "Comptometer" type.
For more information about the history and families of Plus and Sumlock mechanical calculators go to the page Introduction to Plus & Sumlock Mechanical Calculators.

Sumlock 912/S

Bell Punch Sumlock 912/S Sterling Currency calculator.

Petter Mechanical Calculators

The Petter model was the basis of the Bell Punch models. Bell Punch bought the design and rights:

  • Petometer - Abbreviated, 9-column, decimal adding machine.

Bell Punch Mechanical Calculators

The early Petter based models were introduced by Bell Punch in 1939 under the name "Plus Adder":

  • Plus Adder - Abbreviated, 6-column, decimal adding machine.
  • Plus Adder A - Abbreviated, 9-column, Sterling currency adding machine with farthings.
  • Plus Adder B - Abbreviated, 9-column, Sterling currency adding machine.
  • Plus Adder DA - Abbreviated, 9-column, decimal currency adding machine.
  • Plus Adder S - Abbreviated, 9-column, Sterling currency adding machine.
  • Plus Adder SJ - Abbreviated, 9-column, Sterling currency adding machine.
  • Plus Adder ST - Abbreviated, 12-column, Sterling currency adding machine.

These are all abbreviated keyboard models, that is they only have keys 1 to 5 in any column. To add a number higher than 5 then the operator has to press first one key and then another in that column which add up to the required number.

In 1940 a larger, full keyboard (with numbers 1 to 9 in each column), machine under the name "Sumlock" was added to the range, and a separate company, London Computator Corporation, Limited, was incorporated to deal more efficiently with the sales side of the calculators.

In 1950 the name of London Computator Ltd. was changed to Sumlock Limited, and this in turn became Sumlock Comptometer Limited in 1961 when the British operation of Comptometer Corporation was merged.

List of later Plus, Sumlock, and Bell Punch manufactured Comptometer models.
The first number denotes the maximum number of keys in a column, and the second and third numbers denote the number of columns of keys. The letter denotes the type of machine:

  • Plus 506/C - Decimal Currency calculator.
  • Plus 506/D - Decimal calculator.
  • Plus 506/F - Sterling currency calculator with farthings keys.
  • Plus 506/T - Time calculator
  • Plus 509/C - Decimal Currency calculator.
  • Plus 509/D - Decimal calculator.
  • Plus 509/LD - Decimal calculator.
  • Plus 509/F - Sterling currency calculator, with farthing keys.
  • Plus 509/HD - Decimal calculator with 1/2 key.
  • Plus 509/S - Sterling currency calculator.
  • Plus 509/SP - Imperial-Weight calculator.
  • Plus 509/T - Time calculator
  • Plus 509/Y - Imperial-Weight calculator.
  • Plus 512/C - Decimal Currency calculator.
  • Plus 512/S - Sterling Currency calculator.
  • Plusograph - Decimal/Sterling Currency add-lister. see the Calculators made by others section.
  • Sumlock 906/C - Decimal Currency calculator.
  • Sumlock 909/C - Decimal Currency calculator.
  • Sumlock 909/CK - Decimal Currency calculator.
  • Sumlock 912/F - Sterling Currency calculator, with farthing keys.
  • Sumlock 912/S - Sterling Currency calculator.
  • Sumlock 912/Y - Imperial-Weight calculator.
  • Sumlock 913/CP/S - Sterling Currency calculator with Certopost verification device.
  • Sumlomatic - Sterling currency calculator.
  • Automaticket Check Adder - Sterling currency calculator, with farthing keys.
  • Comptometer 992
  • Comptometer 993 - Comptomatic.
  • Comptometer 993e - Electric.
  • Comptometer 993m - Manual, Sterling Currency calculator.
  • Comptometer 993s - Electric, decimal calculator with storage (memory).

Note that the model designations of these machines, especially the Plus Adder models and the London Computator Corporation models, are not fully understood but from evidence are as listed. See the Introduction to the Calculators for more information.

A Selection of the Mechanical Calculators

Click on a picture for more details and more, bigger, pictures.




The early Plus Adders

Plus Adder

Plus Adder B

Plus Adder S
Plus Adder

Plus Adder D (converted)

Plus Adder DA

Plus Adder D (converted)
Plus Adder DA

Plus Adder S

Plus Adder SJ

Plus Adder S Plus Adder SJ

Plus Adder ST

Plus Adder ST

Calculators distributed by London Computator Corporation

A Bell Punch subsidiary which was renamed Sumlock Ltd. in 1950.

London Computator Corporation 509/S

London Computator Corporation 912/S

London Computator Corp 509/S London Computator Corp 912/S

Calculators distributed by Sumlock Ltd. and Sumlock Comptometer Ltd.

A Bell Punch subsidiary, Sumlock Ltd. was renamed Sumlock Comptometer Ltd. in 1961.

Plus 506/D

Plus 506/F

Plus 506/D
Plus 506/F

Plus 506/T time calculator

Plus 509/C

Plus 509/C
Plus 506/T

Plus 509/D

Plus 509/F Sterling Currency Calculator

Plus 509/D
Plus 509/F

Automaticket Check Adder Sterling Currency Calculator

Plus 509/S Sterling Currency Calculator

Plus 509/F Plus 509/S

Plus 509/SP Imperial-Weight calculator

Plus 509/Y Imperial-Weight calculator

Plus 509 Imperial-Weight calculator
Plus 509/SP

Plus 509/T time calculator

Plus 509/T

Plus 512/S Sterling currency calculator

Plus 512/S

Sumlock 912/F Sterling currency calculator with farthing keys.

 Sumlock 912/S Sterling currency calculator

Sumlock 912/F
Sumlock 912/S

Sumlock 912/Y Imperial-Weight calculator

Sumlock 913/CP/S Sterling currency calculator with Certopost verification device

Sumlock 912/Y
Sumlock 913/CP/S

Sumlock Sumlomatic


Sumlock Comptometer 993m Sterling currency calculator

Sumlock Comptometer 993s decimal calculator

Sumlock Comptometer 993s
Comptometer 993m

The Bell Punch Company & the Development of the Anita Calculator
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Text & photographs copyright © 2002 - 2015 Nigel Tout, except where noted otherwise.