Plus & Sumlock Mechanical Calculators
PLUS 509/D
Plus model 509/D
Simple "Comptometer" type adder.
This is a direct action keyboard calculator of the "comptometer" type. It has an abbreviated keyboard (keys up to 5) and is designed for decimal calculations.
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 mechancal calculators.
The label showing that this machine was made by 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.
