Plus & Sumlock Mechanical Calculators
Plus Adder ST
Plus Adder ST
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 £123,456,789 17s 10d.
305 x 149 x 89 mm. (12" x 5.9" x 3.5").
Made in England.
As with the Bakelite bodied Plus Adders, on the bottom of this calculator there is a list 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).
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 thin sheet metal. It is not known whether the sheet metal casing or the Bakelite casing came first - if you have any information about this please let me know.
