Plus & Sumlock Mechanical Calculators 

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.. The keyboard of this machine has keys with, from the left, 7 columns of Hours keys, and 2 columns of Minutes keys. 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. 


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