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 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. Was this sheet metal casing a war-time economy measure, releasing Bakelite for more important uses, or was it a quick way to meet demand for a 12-column machine without going to the
expense of making the tooling for the larger bakelite moulding ? If you have any information about this please let me know.
The mechanism of these machines operates on the
downwards stroke of the keys and there is no interlocking between the keys to prevent more than one key in a column being inadvertently pressed at the same time.
