Home:  Office: COMPTOMETER CALCULATOR 509/S, 1950's


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This Model No 509/S/94.317 and models like this one were leased in large numbers by companies such as Sumloc Comptometer, until electronic adding machines replaced them. The machines worked by adding only and other functions were completed by progressive use of the keys, ladies often complained that the long strokes of pushing down the keys broke their finger nails. The curator of this museum used this model when she worked at Marks and Spencer in the 1960's and had the reputation of being the quickest operator in the office. The Plus and Sumlock are machines of the "Comptometer" type; the Sumlock being the full-keyboard version and the Plus the abbreviated-keyboard version. They are intended primarily for addition, but can also be used for subtraction, multiplication and division using learned techniques.
The main feature of this type of machine is that it has a full-keyboard and is "key driven", which means that pressing any key immediately adds the number on that key to the number displayed in that column, with carrying to the next column taking place where necessary.
The machine is designed so that keys in different columns can be pressed simultaneously. This means to add the cost of several identical items the operator arranges his or her fingers on the required keys and then depresses them all simultaneously the number of times for the number of items. Working in this way this type of machine is much faster than a 10-key type of machine where each digit has to be entered successively.
In 1960, the Bell Punch Company bought the British rights to the Comptometer design and trademark, and continued its development. In 1961, Sumlock, a division of the Bell Punch Company, was renamed The Sumlock Comptometer Ltd, and began marketing the first all-electronic desktop calculator, the ANITA Mark VII. The entire calculator division of the Bell Punch Company was bought by Rockwell International in 1973. Unfortunately they exited the calculator business in 1976 and shut down all operations.
Not all Comptometers are of Bell Punch origin. Many were made and marketed by others; whether Bell Punch had their own manufacturing base for these machines is not clear. See Item A1157.

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