Plus & Sumlock Mechanical Calculators
Plus 506/D

PLUS 506/D

PLUS model 506/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 506/D where the 5 denotes the abbreviated keyboard (keys up to 5), the 06 denotes the 6 columns of keys, and the D denotes a Decimal version.

185 mm x 180 mm x 127 mm. (7.25" x  7" x 5").

The angular style casing of the machine illustrated was introduced in 1958.

One of the more minimalist calculators made. Has 6 decades of keys, with each decade numbered from 1 to 5, so to enter a number between 6 and 9 two keys have to be pressed in succession in that column.  The knob on the right is for clearing the total.

Made in England by Bell Punch Co. Ltd. and distributed by Sumlock Compometer Ltd.

The machine illustrated has serial number 506/D/815.357.


The bottom of the machine.


Many patents are listed on the label.

B.S. 1909 probably relates to British Standard 1909.

Capable really only of adding lists of numbers to 9,999,999, but capable of doing this quickly and accurately (and cheaply !).

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.