Plus & Sumlock Mechanical Calculators
PLUS 509/D

PLUS 509

Plus model 509/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.

It is a model 509/D where the 5 denotes the abbreviated keyboard (keys up to 5), the 09 denotes the 9 columns of keys, and the D denotes a Decimal version.

235 x 182 x 120 mm (9.25" x 7.2" x 4.75").

The machine illustrated has serial number 509/D/892604.

Made in or after 1966, when Sumlock Anita Electronics was formed to manufacture the electronic and mechanical calculators.


The label showing that this is a later machine, made when the manufacturing company was known as Sumlock Anita Electronics Ltd.

There are excellent photographs and descriptions of the Plus Adder mechanism at John Wolff's Web Museum site. These are accessed from the Comptometers and Key-Driven Calculators section on that site.

Click here to go to the Vintage Calculators Web Museum

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