Plus & Sumlock Mechanical Calculators
Plus Adder D

Plus Adder D

Plus Adder D

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.

The photograph above shows a total of 12,345,678.

230 x 153 x 100 mm. (9" x  6" x 3.9").

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 patents listed underneath the machine in the photograph below.
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.

This machine is unusual in two ways:

Cover removed

With cover removed.


Close up of the plate on the bottom with the original model type "S" scratched out and model type "D" substituted.
Apparently this machine was converted to a decimal type "D" from a type "S", for use with the old British £sd currency.

All of the U.K. patents listed on the plate were applied for  by¬  Guy Bazeley Petter and Petters Limited of Westland Works, Yeovil,  Somerset, from whom Bell Punch acquired them.
The  application for the first, 208,232, was submitted on September 14th  1922, and the application for the last, 413,373, was submitted on  January 20th 1933.

Click here to go to the Vintage Calculators Web Museum

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