**Plus & SumlockMechanical 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.

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 D*- Abbreviated, 9-column, decimal 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.

- London Computator Corporation
*509/S*- Abbreviated Sterling currency adding machine. - London Computator Corporation
*509/MD3*- Abbreviated decimal adding machine. - London Computator Corporation
*Sumlock 912/S*- Sterling currency adding machine. - London Computator Corporation
*912/MD3*- Decimal adding machine.

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:

- 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. - Automaticket
*Check Adder*- Sterling currency calculator, with farthing keys.

*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 keyboards):

- Sumlomatic - Has a multiplication register.
- Comptometer
*992*- Electrically powered. - Comptometer
*993*- Comptomatic. - Comptometer
*993e*- Electrically powered. - Comptometer
*993m*- Manually powered. - Comptometer
*993s*- Electrically powered, with storage (memory).

Specialist models:

- Bell Punch Analyser - A basic adding machine with a small bank of counters.

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.*

**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.
**

**Specialist Calculators**

The Bell Punch Company & the Development of the Anita Calculator

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Text & photographs copyright © 2002 - 2017 Nigel Tout, except where noted otherwise.