Plus Adder D
Decimal, 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
The 4 and 5 keys in the left-most column are used for subtraction using the "nines-complement" method.
The photograph above shows a total of 123,456.78.
230 x 153 x 105 mm.. (9" x 6" x 4.1").
Made in England.
This particular example is missing the mechanism in the left-most column.
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. See the patents listed on the Plus Adder S machine.
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.