Napier's Curve, Diagram. Curved line drawn on a specially designed diagram and passing through a limited number of points on which deviation of compass has been ascertained. This facilitates the determination of deviations on points for which no observation has been made.
Napier's Rules of Circular Parts. Diagrammatic arrangement of five parts, or their complements, of a right-angled or quadrantal spherical triangle, the right angle or 90° side being disregarded, in five sections of a circle. If these be put in the rotation of their occurrence, an unknown part can be found from the other parts; the rule being that sine of middle part equals product of tangents of adjacent parts, or product of cosines of opposite parts.
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