Plus & Sumlock Mechanical Calculators
Plus Adder SJ
Plus Adder SJ
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.
This is a very small machine of this type and can add up to just £999 19s 11d.
One of the first Plus models, which were based on the Petters design that Bell Punch bought from that company in 1936.
Made in England.
The case is unusual in being made of Bakelite. 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.
On the bottom is a list of patents, see photograph below. The British ones had been 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 1922 and the others in the early 1930s.
This is one of the first Bell Punch calculators based on the Petters design that Bell Punch bought from that company.
