Operating a Comptometer

Plus & Sumlock Mechanical Calculators
PLUS 509/T Time Calculator

PLUS 509 Time Calculator

Plus model 509/T/828599 Time "Comptometer".

This is a direct action keyboard calculator of the "comptometer" type. It has an abbreviated keyboard (keys up to 5) and is designed for calculations in hours and minutes.

235 x 182 x 120 mm (9.25" x 7.2" x 4.75").

This casing style was introduced in 1958..
Made by Bell Punch Co. Ltd. in Britain, distributed by Sumlock Ltd.

The keyboard of this machine has keys with, from the left, 7 columns of Hours keys, and 2 columns of Minutes keys.
Although from the outside the machine is similar to a normal decimal machine, inside it is geared to carry over when the second column from the right reaches 6, i.e. 60 minutes carries over to 1 hour.

To enter a number above 5 the operator has to press two keys in that column, one after the other, which add up to the number required.

The machine in the photographs above and below displays the total of 123 Hours and 55 minutes. By adding 5 minutes (i.e. pressing the 5 key in the right hand column) would produce the result 124 hours 00 mins.


This machine would have been very useful in the wages department of a company, totalling the hours worked.

Time has not been metricated, so there is still the need to calculate in hours and minutes. Electronic calculators are available for the television industry which can calculate in hours, minutes, seconds, and frames for various broadcast standards.

Origins of Bell Punch Co.
All Change at Bell Punch
Development of Anita 1
Development of Anita 2
Anita is Launched
At work with Anita
National Calculating Service
Anita Developed Further
Anita at its Zenith
The Rockwell Connection
Demise of Anita & Bell Punch
Mechanical Calculators
Early Anita Desktop Calculators
Transitors & Integrated Circuits
Anita LSI Desk Calculators
Anita Hand-held Calculators
Rockwell-Anita Calculators
Calculators made by others
The Technology Explained
Operating a Comptometer
Old Sterling Currency, £sd
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Plus & Sumlock Mechanical Calculators

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Sumlock Comptometer 993m
Sumlock Comptometer 993s

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Text & photographs copyright © 2002, 2003 Nigel Tout, except where noted otherwise.