Plus & Sumlock Mechanical Calculators
PLUS 509/C

PLUS 509

Plus model 509/C

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/C where the 5 denotes the abbreviated keyboard (keys up to 5), the 09 denotes the 9 columns of keys, and the C probably denotes a Currency version (the two right-most columns are in the same colour for the pence or cents, or similar, of a decimal currency).

The photograph of this model has been kindly supplied by Wilfried Denz who has a website featuring old calculators at

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.