Plus & Sumlock Mechanical Calculators
Plus Adder
Plus Adder
Decimal, key-driven ("Comptometer") type, with abbreviated keyboard (only has keys 1 to 5). To enter a number greater than 5 two keys have to be pressed in succession in that column.
The lever on the right is for clearing the
total.
This example does not have a model letter stamped on the manufacturer's plate underneath. If you have any information about the model letters of these early Plus Adders please get in touch.
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. Some of the patents awarded to Petters are listed on the bottom of the 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.
Photographs of this model have been kindly supplied by Wilfried Denz who has a website featuring old calculators at http://www.rechnen-ohne-strom.de/.
Close up of the plate on the bottom without a model type displayed.
Plus & Sumlock Mechanical Calculators
Text & photographs copyright © 2002 - 2023 Nigel Tout, except where noted otherwise.