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176 to 180 of 227 glossary terms
Saints' days: anniversary days for Christian saints.
scaphe dial: sundial where the hour lines are marked on a concave hemisphere or part hemisphere.
sector: calculating instrument using pairs of lines on the faces of two hinged arms, see article on the sector.
sexagenarium: an instrument in the form of a volvelle for planetary calculations.
shadow square: a form of geometrical quadrant, where two sides of a square are divided into equal parts and a plumb line or alidade from the opposite corner is used for measuring angles in terms of ratios (that is, tangents). Where a plumb line is used, one side has a pair of fixed sights. The name comes from the fact that a measurement of the altitude of the sun, expressed as a ratio, applied to the length of the shadow cast by an upright structure, yields its height. See also under astrolabe.
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