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Patented by Edwin Thacher (1839-1920) in 1881, this device performed a variety of arithmetical calculations rapidly and accurately. The instrument consists of a cylinder four inches in diameter and 18 inches long, which revolves in an open framework composed of 20 angular bars held between two metal rings. The cylinder bears a scale corresponding to the scale of the slide rule, which is duplicated on the exposed sides of the bars. Results can be obtained to the fourth, and usually to the fifth, place of figures. |
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