Plus & Sumlock Mechanical Calculators
PLUS 509/S Sterling Currency Calculator

Plus model 509/S

Sterling currency, key-driven ("Comptometer") type, with abbreviated keyboard (only has keys 1 to 5).  To enter a number greater than 5 two or three keys have to be pressed in succession in that column.

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

The calculator in the photograph above displays the total:
£1,234,567 17s 11d.

230 x 190 x 124 mm (9" x 7.5" x 4.9").

This casing style was replaced by a more modern version in 1958.
Made by Bell Punch Co. Ltd. in Britain, distributed by Sumlock Ltd.

The machine illustrated has serial number 509/S/95.899.

With the cover removed.

With the cover removed.


Rear of the calculator.


This older style casing has the maker's badge on the back, secured in a recess with adhesive. Often the adhesive weakens and the badge falls off and is missing.

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.