Plus & Sumlock
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.
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 some 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
Calculators distributed by London Computator Corporation
A Bell Punch subsidiary which was renamed Sumlock Ltd. in 1950.
Calculators distributed by Sumlock Ltd. and Sumlock Comptometer Ltd.
A Bell Punch subsidiary, Sumlock Ltd. was renamed Sumlock Comptometer Ltd. in 1961.
Text & photographs copyright © 2002 - 2017 Nigel Tout, except where noted otherwise.