Bell Punch "PLUS Rapid Adder", Model A, S/N 3332
9 columns, Sterling currency (no farthings)
Dimensions: 8-1/2"W x 6"D x 4"H
Weight: 5 pounds
Manufactured: Bell Punch Company, England, 1936-
The Bell Punch Company (BPC) was established in London in 1878, and took its name from its original product - a bus conductor's registering ticket punch. The company expanded into ticket printing and issuing equipment for buses, trams, and cinemas, racecourse betting tickets, and taxi meters. Their activities were generally related to "cash control systems", and were coordinated through a holding company "Control Systems Ltd" from 1927. Both companies established branches in Australia and other Commonwealth countries.
In 1936 the company purchased the rights to a small half-keyboard adding machine which was sold as the "PLUS Rapid Adder". Larger full-keyboard versions with Comptometer-style safety mechanisms were marketed under the name "Sumlock". The London Computator Corporation was established in 1940 to handle the calculator business, but the nameplate soon reverted to The Bell Punch Company.
The PLUS and Sumlock machines were very popular in Britain and Commonwealth countries. They continued in production for almost 40 years, until replaced by computers and electronic calculators in the 1970s.
In the late 1950s the Bell Punch Company acquired the British rights to the Comptometer name from the ailing Comptometer Corporation (formerly Felt & Tarrant) of Chicago. When Comptometer production ended in 1961, the Bell Punch Company exported re-badged Sumlock machines to America to be sold as new-model Comptometers.
In the mid-50s the company started to introduce electronics into its product lines, and began work on an electronic calculator. The world's first commercial electronic calculator, the Sumlock "Anita", was introduced in 1961. The Sumlock Anita Electronics Company was established in 1966 to handle the calculator business (including the mechanical calculators), but was taken over by the American Rockwell organisation in 1973. Rockwell soon lost interest in calculators in favour of their aerospace business, and Sumlock Anita was effectively disbanded in 1976. The Bell Punch Company continued on with its traditional ticketing products, until it too was finally broken up and sold in 1986.
The original mechanism of the PLUS Rapid Adder was designed by Guy Petter of the Petter oil engine family during the 1920s. The design was acquired by the Bell Punch Company in 1936, and was put into immediate production. A greatly improved mechanism was developed by Christopher Webb of Bell Punch in 1938, and formed the basis of all subsequent models.
The PLUS adder was a half-keyboard machine with keys from 1 to 5 only. It was common practice among skilled Comptometer operators to use only the lower half of the keyboard for addition, as it was found to be less tiring to enter (eg) 8 by striking 4 twice, than to move one's whole arm to make a deeper and firmer stroke on the 8 key. The half-keyboard machines were much smaller, lighter, and cheaper than the full-keyboard models, and were entirely satisfactory provided one had no need for anything beyond simple addition.
The internal mechanism of the PLUS adder was quite different to both the Comptometer and the Burroughs Calculator, and provided a reasonable degree of error protection. The machine would not register if a key was not fully depressed (although there was no error indication or lockout), and would not repeat a keystroke until the key had fully risen. A definite start-from-clear signal was provided by the clearing lever.
Click on the photos below for larger illustrations.
Bell Punch "PLUS Rapid Adder", Model A, S/N 3332
9 columns, Sterling currency (no farthings)
Dimensions: 8-1/2"W x 6"D x 4"H
Weight: 5 pounds
Manufactured: Bell Punch Company, England, 1936-
An early PLUS Rapid Adder (Model A) for Sterling currency, in a black bakelite case.
The nameplate on the base of the machine lists three of the US patents that were filed by Guy Petter from 1923 to 1931.The mechanism operates on the downwards keystroke, with the register advancing in proportion to the depth of travel. A "duplexing " mechanism allows keys in adjacent columns to be operated simultaneously, but there is no protection against incomplete keystrokes. The clearing lever on the right-hand side is pushed downwards to advance the register dials to zero.
Bell Punch "PLUS Rapid Adder", Model 509/S, S/N LC/509/S/3774
9 columns (10 digits), Sterling currency (no farthings)
Dimensions: 9-1/4"W x 7-1/2"D x 5"H
Weight: 9 pounds
Manufactured: London Computator Corporation, England, about 1940
A 9-column PLUS adder for Sterling currency, produced by the London Computator Corporation in about 1940 (serial number 3774).
The revised mechanism in this (and subsequent) machines operates on the upwards stroke of the key, and provides protection against incomplete strokes in both directions. The small clearing lever on the right-hand side has a very short movement. It remains latched in position until the first keystroke of the next calculation to provide a "start from clear" indication. The numeral wheels return backwards to zero when the clearing lever is operated. The mechanism sits on a flat steel baseplate with substantial rubber feet, and has a die-cast alloy cover with external lifting handles.
Follow the link above for a detailed technical description of the Plus internal mechanism.
Bell Punch "PLUS Rapid Adder", Model 512/F, S/N 512/F/90075
12 columns, Sterling currency (with farthings)
Dimensions: 11-1/2"W x 7-1/2"D x 5"H
Weight: 11 pounds
Manufactured: London Computator Corporation, England, 1940s
A 12-column PLUS adder for Sterling currency, with farthings.
The PLUS machines were made in versions with 6, 9, and 12 columns. They could be supplied for Sterling currency (with or without farthings), decimal currency, feet and inches, hours, minutes, and seconds, and even tons, hundredweight, and quarters.
The model numbers show the number of keys and columns (5-09, 5-12, etc), the denominations (S for Sterling, F for farthings, C for decimal, etc), and a consecutive serial number.
Bell Punch "PLUS Rapid Adder", Model 506/S, S/N 506/S/43769Q
6 columns, Sterling currency (no farthings)
Dimensions: 7"W x 7-1/2"D x 5"H
Weight: 6-1/2 pounds
Manufactured: Bell Punch Company, London, 1950s
A compact 6-column PLUS adder for Sterling currency.
The PLUS machines from the 1950s had a bright green hammertone finish and a re-styled clearing handle. The individual glued-on letters forming the "PLUS" name were replaced with a one-piece badge.
Bell Punch "PLUS Rapid Adder", S/N 509/S/68,355
9 columns (10 digits), converted to decimal currency
Dimensions: 9-1/4"W x 7-1/2"D x 5"H
Weight: 9 pounds
Manufactured: Bell Punch Company, England, 1950s
This 9-column machine was originally built for Sterling currency (the "S" in the serial number), but was re-manufactured in decimal during Australia's currency conversion in 1966. While official factory conversions used all new parts, some repair shops would simply dis-assemble nine Sterling machines and re-build them as seven decimal machines, replacing the ten-shillings and pence columns with decimal columns from the two sacrificial machines. The colour groupings on the keyboard and registers did not always match the factory originals.
Bell Punch "PLUS Rapid Adder", S/N 509/F/820,425
9 columns (10 digits), converted to decimal currency
Dimensions: 9-1/2"W x 7-1/2"D x 5"H
Weight: 7 pounds
Manufactured: Bell Punch Company, England
A late-model Plus adder in a re-styled case, incorporating a light-weight die-cast baseplate with inbuilt lifting grips. The cylindrical keys extend through individual holes in the one-piece top cover. The clearing handle has been relocated to the top front corner of the machine. The pressed-metal gears in the register and carry mechanism have been replaced with moulded plastic, but the mechanism is otherwise identical to the earlier models.
This machine was originally built for Sterling currency with farthings, but has been converted to decimal with authentic colour groupings.
Bell Punch "PLUS Rapid Adder", S/N 509/C/859,127
9 columns (10 digits), decimal currency
Dimensions: 9-1/2"W x 7-1/2"D x 5"H
Weight: 7 pounds
Manufactured: Bell Punch Company, England, 1960s
The final version of the Plus adder was finished in a colour that varies from beige to pink, depending on the light and the time of day. This machine was factory-built for decimal currency, and shows the original colour groupings in the keyboard and register.
During the 1940s Christopher Webb of The Bell Punch Company developed a line of full-keyboard key-driven machines based on an extended version of his improved "Plus" mechanism. The name "Sumlock" was applied to these later machines which included a Comptometer-style locking mechanism to guard against incomplete keystrokes. If a key is not fully depressed, the entry will not register, the key will not rise, and the rest of the keyboard will immediately lock. The operator can complete the keystroke on the conspicuous half-risen key, clear the lock by pressing the release lever, and continue with normal operation.
The Sumlock machine also has protection against incomplete upstrokes, and includes a start-from-clear signal and cutoff levers for use in subtraction. The machine is functionally equivalent to the Felt & Tarrant Comptometer, although based on an entirely different mechanism.
Webb continued to develop the Sumlock machine during the 1950s, adding an electric motor drive, a second "grand-total" register, and finally a semi-automatic multiplier mechanism.
In the late 1950s the ailing Comptometer Corporation sold the British rights to the Comptometer name to the Bell Punch Company, and imported Sumlock machines to be sold as new-model Comptometers. The machines were branded "Sumlock Comptometer" in Britain, "Sumlock" in the BPC export markets, and in "Comptometer" in America. The machines reached Australia through both the Bell Punch and the Felt & Tarrant distributors, resulting in two competing lines that were identical in all respects, apart from the name badge and the colour scheme. (Compare the machines below with those on the Felt & Tarrant page).
Sumlock comptometer, Model 912, S/N 912/S/104673
12 columns (13 digits), Sterling currency (with farthings)
Dimensions: 12-1/2"W x 13"D x 6"H
Weight: 17 pounds
Manufactured: Bell Punch Company, England, 1940s
An early 12-column Sumlock comptometer for Sterling currency, with farthings, but with no 10 or 11 keys in the pence column. The practice of using multiple keystrokes made the keys unnecesary for addition, but their absence did introduce some minor complications in subtraction.
The machine is based on the improved PLUS mechanism, which has been extended to provide Comptometer-style error detection and keyboard locking. The lock release is via the small red button at the right-hand rear.
Sumlock comptometer, Model 912, S/N 912/S/4A/130611
12 columns (13 digits), decimal currency (converted)
Dimensions: 13"W x 12-1/2"D x 6"H
Weight: 17 pounds
Manufactured: Bell Punch Company, England, 1950s
A 12-column machine from the 1950s, in a re-styled casing with new cylindrical keytops.
The clearing lever has been relocated to the front right corner, and now performs two separate functions. It is drawn forward to clear the register, or pushed rearward to clear the keyboard lock.
This machine has been converted from Sterling to decimal currency.
Sumlock dual-register comptometer, Model 912, S/N 912/S/Va/510003B
12 columns (13 digits), Sterling, dual register, electric
Dimensions: 13"W x 13"D x 8"H
Weight: 29 pounds
Manufactured: Bell Punch Company, England, 1953-
A 12-column machine for Sterling currency (no farthings), with an electric motor drive and a second "grand total" register at the rear.
The powered driving mechanism is described in Webb's US Patent 2756932, and the dual register in 2773647, both filed in 1951.
Sumlock "Figure-flow" comptometer, S/N 909/IVB/C/143,875
9 columns (10 digits), decimal currency
Dimensions: 10-1/2"W x 13"D x 6"H
Weight: 14 pounds
Manufactured: Bell Punch Company, England
A 9-column "FigureFlow" comptometer in a re-styled casing. There were no significant changes to the mechanism.
Sumlock "Duolectric" comptometer, Model 912, S/N 912/VZ/C/915277
12 columns (13 digits), decimal, dual register, electric
Dimensions: 13-1/2"W x 14"D x 8"H
Weight: 29 pounds
Manufactured: Bell Punch Company, England
A 12-column dual-register machine for decimal currency in a re-styled casing, now labelled as the Sumlock "Duolectric".
Sumlock "Sumlomatic" comptometer, Model 912/F/VIa, S/N 607490A
12 columns (13 digits), dual register with multiplier, electric
Dimensions: 14"W x 15-1/2"D x 7-1/2"H
Weight: 35 pounds
Manufactured: Bell Punch Company, England, 1959-
The "Sumlomatic" was the final development of the Bell Punch Company's mechanical calculators. It is based on the motor driven dual-register machine, with the addition of a third register and a control mechanism to perform semi-automatic multiplication. The concept is described in Webb's US Patent 2956741, filed in 1955, but the machine did not reach the market until 1959. The Sumlock "Anita" electronic calculator was released the following year.
The illustrations following show some of the labels and logos that are found on Bell Punch machines in Australia. Click on the images for larger versions.
The PLUS Model A nameplate
The nameplate on the underside of an early PLUS Model A gives only the serial number and a list of British and foreign patents.
The three US patents listed were filed by Guy Petter of Yeovil between 1923 and 1931. The machine also contains Petter's duplexing mechanism, which did not receive its US Patent (2142286) until January 1939.
The London Computator Corporation nameplate
The London Computator Corporation was set up in 1940 to handle the Bell Punch calculator products.
This brass nameplate (7" x 3" approx) is screwed to the underside of an early PLUS adder. It gives the name and address of the manufacturer, the addresses and phone numbers of the branches throughout Britain, a list of patent dates, and a 1-year written guarantee.
The four US patents listed are for the Petter mechanism (including the duplex lever), although the machine actually contains the improved Webb mechanism. The US patent for Webb's 1938 improvements was not issued until 1942.
The serial number (3774) is stamped into the nameplate, and also into the right-hand side plate of the mechanism.
The Bell Punch Company nameplate
This steel nameplate is typical of those rivetted to the bottom of machines carrying the Bell Punch brand. It gives rather less information, but much longer lists of patents. This design was used with minor variations from the 1940s to the 1960s.
The "Model Number" consists of the number of rows and columns (509), a type letter (eg S for Sterling), and a consecutive serial number (68,355).
The Sumlock Anita Electronics nameplate
The "Sumlock Anita Electronics Company" was set up in 1966 to handle the Bell Punch range of mechanical and electronic calculators.
This self-adhesive aluminium nameplate is from a late-model PLUS machine that was originally built to add hours, minutes, and seconds. The serial number (890475) is engraved rather than stamped.
The Sumlock - Comptometer Corporation nameplate
This nameplate was used on the Sumlock machines produced for export to the Comptometer Corporation in America.
A bolt-on "Comptometer" badge was used on the front and rear panels of the machine, in the same size and style as the standard "Sumlock" badge. The nameplate underneath has had the manufacturer's name and the British patent details removed, perhaps to disguise its origins, although the standard Sumlock baseplate is still stamped "Made in Great Britain".
PLUS Model A roundel
An embossed paper roundel about 1-1/4" diameter is set into the back panel of the PLUS Model A. The text gives the machine name and the maker's details.
London Computator Corporation Roundel
The London Computator Corporation machines have a larger 1-1/2" roundel finished in gold and blue.
The text on this early version reads:
Guaranteed
Wholly made in England
for the
London Computator Corp'n. Ltd
39, St James's St. London
Bell Punch Company Roundel
This version from a 1950s machine has the Bell Punch Company at the same address. England has since become Great Britain.
Bell Punch A/sia Ltd
A distributor's transfer on the back of a PLUS adder from the 1940s. Bell Punch A/sia Ltd was presumably a subsidiary of The Bell Punch Company, itself a part of (Cash) Control Systems.
"A/sia" is an abbreviation for "Australasia", a fictitious region of the British Empire consisting primarily of Australia and New Zealand. It has nothing to do with Asia.
Control Systems A/sia Pty Ltd
A transfer from Control Systems A/sia Pty Ltd, from a later PLUS adder.
PLUS Training Manual
This training manual for the "PLUS Rapid Adder" was printed in Sydney by the Australian distributors (Control Systems) for use in their operator training schools.
The 12-page booklet has instructions and practice examples for addition and multiplication, covering both general calculations in the decimal system, and currency calculations in Sterling.