Historical information
The "Burroughs Calculator" was a non-printing key-driven machine introduced in 1912 in response to the success of the Felt & Tarrant "Comptometer".
The first Burroughs key-driven machine was very similar to the Comptometer in its external appearance, but was quite different in its internal mechanism, with the register and carry mechanism based on a complex system of planetary gears. It was only about two-thirds of the weight of the Felt & Tarrant machine, and had none of the safety features. In particular, there was no protection against incomplete keystrokes in either direction. The register would simply advance in proportion to the depth of stroke, with no indication of error. However, the price was also about two-thirds of the Comptometer, which made it quite a popular (if dangerous) machine.
(http://home.vicnet.net.au/~wolff/calculators/Burroughs/Burroughs.htm)
The Burroughs Portable Adding Machine introduced in 1925 became the basic design for the adding machine for many years, until the ten key adder was introduced and started to replace it gradually.
The key-driven type machine did not print, and while it was often used as an adding machine, it developed into a special purpose machine in later years. The machine was very fast . The efficient operation of these machines required an experienced operator who often received a high salary.
The machine was produced over a very long period because of its unique capabilities and was often used to verify product delivery lists from delivery routes. Later models of the machine, called a duplex design, could hold a running total in a second set of dial wheels while the primary wheels continued to add and subtotal amounts that could be transferred at any time to the running total.
A side note, Burroughs copied the Felt design for its first models and was sued for patent infringement by Felt and Tarrant who prevailed in the suit. As a result, Burroughs totally redesigned their machine and went on to compete with the Felt machine for decades.
Info from (http://www.burroughsinfo.com/group_d.htm)
Physical description
Black metal low keyboard manual adding machine. The key-driven type machine did not print, and was exceedingly fast and experienced operators could easily outrun an operator on a full keyboard or 10-key adding machine.
The adding machine has a brown leather carry case.
