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:

Bell Punch Mechanical Calculators

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

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:

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 S
Plus Adder D (converted)
Plus Adder DA
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 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/T
Plus 509/C
Plus 509/D
Plus 509/F
Plus 509/F
Plus 509/S
Plus 509/SP
Plus 509 Imperial-Weight calculator

Plus 509/T time calculator

Plus 509/T

Plus 512/S Sterling currency calculator

Plus 512/S
Sumlock 912/F
Sumlock 912/S
Sumlock 912/Y
Sumlock 913/CP/S

Sumlock Sumlomatic

Comptometer 993m
Sumlock Comptometer 993s

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.