Plus & Sumlock Mechanical Calculators
Plus Adder S
Plus Adder S
Sterling currency, 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. The lever on the right is for clearing the total.
The photograph above shows a total of £123,456 17s 11d.
230 x 153 x 105 mm.. (9" x 6" x 4.1").
Made in England.
On the bottom, this calculator has lists of patents, and the three U.S. ones were taken out by Guy Bazeley Petter, with rights assigned to Petters, Limited, Yeovil, England (the internal combustion
engine manufacturer). One of the patents had been applied for in Great Britain in 1923 and the other two in 1930.
This is almost certainly one of the first Bell Punch calculators, which were based on the Petters design that
Bell Punch bought from that company in 1936.
The case is unusual in being made of Bakelite. These models appear to have been superceded by the metal-bodied London Computator and Plus machines by 1948, since is is these
models which are shown in photographs of Sumlock exhibition stands of this time.
