(n) a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists, Syn. dioptre
{ ‖ } n. [ L. dioptra, fr. Gr. &unr_;. See 2d Dioptric. ] An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc. [ 1913 Webster ]
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