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.
Plus 509/LD abbreviated-keyboard decimal calculator.
Bell Punch Sumlock 912/S full-keyboard Sterling Currency calculator.
Petter Mechanical Calculators
The basis of the Bell Punch mechanical calculator models is the mechanism patented by Guy Bazeley Petter, of the famous Petter engineering company. Bell Punch bought the design and rights of the mechanism:
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-type" 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. Some of the machines distributed by London Computator Ltd. have the letters 'LC/' before the model number. Manually operated machines were often termed "Figureflow".
When the old Sterling Currency (」sd) was superseded by Decimal Currency it was common for old Sterling machines to be converted to Decimal machines and these could retain the old label with its '/S/' Sterling Currency designation. Sometimes the Sterling to Decimal conversion of a machine was done crudely by someone simply by removing the shillings and pence columns of keys and fitting a blanking plate.
Sales brochure for Plus machines (pdf format).
Sales brochure for Sumlock machines (pdf format).
Later, top of the range models (most were available with decimal or Sterling currency (」sd) keyboards):
Specialist models:
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 Mechanical Calculators for more information.
A Selection of the Mechanical Calculators
Click on a picture for more details and more, bigger, pictures.
Petometer
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.
After 1961 the Bell Punch Co. also produced mechanical machines for Comptometer Corporation of the U.S.A.
Initially the naming of the models originating from both companies is a little confusing. For example:
Some Sumlock machines can be found labelled 'Comptometer' and with a different model number.
For example:
Further information about these 'Comptometer' models can be found on John Wolff's website at http://www.johnwolff.id.au/calculators/Comptometer/FT.htm#UK.
The journal 'Office Magazine' in January 1962 gave a list and a brief description of the Sumlock Comptometer mechanical machines at this time[1]:
"
Figureflow Comptometer GBP 」160 Hand driven 1 register
Sumlock Unilectric GBP 」195
Electric 1 register
992 Comptometer GBP 」208
Electric 1 register
Duolectric Comptometer GBP 」285 Electric 2
registers
Sumlomatic GBP 」330
Electric 3 registers (multiplier register)
The simplest Sumlock model is the Figureflow Comptometer. The sterling model has a keyboard capacity of 」999,999,999 19s 11d. Each column has its own clearance lever and
there is a clearance control on the right of the machine.
The same machine, but electrified, is the Unilectric Comptometer and a slightly more elaborate model, the 992. The two-register machine, the
Duoelectric Comptometer has, as is necessary, a transfer control. The second register used for automatic accumulation of separate products or subtotals also provides a means of direct subtraction because one register can be
subtracted from the other.
A development of the key-driven machine is the Sumlomatic, which has a multiplier register as well as the two registers of the Duolectric. Apart from the necessary
multiplier-transfer lever, the machine also has a constant-factor control lever. This retains a figure in the multiplier register as a constant factor. The Sumlomatic is in reality a combined rotary and key-driven
machine having a keyboard, a product register, a product-storage register and a rotary mechanism. Where the volume of division work is relatively high and there is a large number of different divisors, division is done by
complementary addition. If the volume is low and the number of different divisors reduced, reciprocals are used."
The 993 Family
The mechanical models were soon rationalised and were given model numbers in the 993 series.
The journal 'Office Magazine' in October 1963, reporting about the Business Efficiency Exhibition, stated[2]:
"Sumlock Comptometer Ltd.
Four models in the 993 range introduced earlier this year will be featured on this stand. They are the 993s electric storage model, costing 」265, the 993e electric single register model, price 」195, the 993m manual
register model (」160) and the 99s Comptomatic, an electric storage model with automatic multiplication, accumulation and direct subtraction, which sells for 」330. Each of these machines has a capacity of thirteen answer
figures, can give addition answers directly in strerling and provides for all four arithmetical processes.
In addition, examples of the Comptograph Model 101 and Model 101WS, selling at 」87 10s 0d and 」180
respectively, and the non-listing Plus Rapid Adder range, priced from 」35 to 」50 will be on view, as will the Anita electronic calculator."
The machines of the 993 family were the last new designs of mechanical "Comptometer"-type machines from Bell Punch, and probably the last in the world.
These models have a new design of casing which is more angular.
Below is an advertisement for the 993 family from February 1964:
Specialist Calculators
For more information about the history and families of Plus and Sumlock mechanical calculators go to the page Introduction to Plus & Sumlock Mechanical Calculators.
Reference:
The Bell Punch Company & the Development of the Anita Calculator
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Text & photographs copyright © 2002 - 2023 Nigel Tout, except where noted otherwise.
