NATIONAL PHYSICAL LABORATORY (C) CROWN COPYRIGHT / SCIENCE PHOTO LIBRARY NATIONAL PHYSICAL LABORATORY (C) CROWN COPYRIGHT / SCIENCE PHOTO LIBRARY
Early 20th century calculator. This hand calculator, the Brunsviga 20, is mechanically operated by a handcrank (right). Addition and subtraction sums were performed in a single operation, but multiplication and division were accomplished by repeated mechanical additions and subtractions. The German company Brunsviga introduced their calculators in 1885 and had produced over 20,000 machines by 1912.
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