Plus & Sumlock Mechanical Calculators
Plus 506/F

PLUS model 506/F.

Simple "Comptometer" type adder for old £sd Sterling currency, with farthings.

170 mm x 190 mm x 118 mm. (6.7" x  7.5" x 4.6").

One of the more minimalist calculators made. Has 2 decades of £ keys, shillings, pence, and farthings (quarters of a penny) keys, with each decade numbered from 1 to 5. To enter a number between 6 and 9 (or 11 in the case of the pence column) two keys have to be pressed in succession in that column. The knob on the right is for clearing the total.
The machine illustrated shows the total £12 17s 11 3/4d.

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

The machine illustrated has serial number 506/F/45.74, and has the older, rounded style casing. The farthing ceased to be legal currency in Britain in 1961, when this model would have become obsolete.

Capable really only of adding lists of amounts to £999 19s 11 3/4d, 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 - 2008 Nigel Tout, except where noted otherwise.