Plus & Sumlock Mechanical Calculators
Plus Adder B

Plus Adder B

Plus Adder B

Sterling Currency, key-driven ("Comptometer") type, with abbreviated keyboard (only has keys 1 to 5). To enter a number greater than 5 two or three keys have to be pressed in succession in that column.
The lever on the right is for clearing the total.
The 4 and 5 keys in the left-most column are used for subtraction using the "nines-complement" method.

The photograph above shows a total of £12,345 17s 6d.

230 x 153 x 105 mm.. (9" x  6" x 4.1").

Made in England.

This is one of the first Bell Punch calculators, which were based on the Petters design that Bell Punch bought from that company in 1936. See the page on the Petometer and also the patents listed on the Plus Adder S machine.
The case is unusual in being made of Bakelite. The mechanism of these machines operates on the downwards stroke of the keys and there is no interlocking between the keys to prevent more than one key in a column being inadvertently pressed at the same time.


Close up of the manufacturer's badge to the left of the keyboard.

Cover removed

With cover removed, showing the mechanism.


Close up of the plate on the bottom with the model type "B".

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Text & photographs copyright © 2002 - 2023 Nigel Tout, except where noted otherwise.