What is the meaning of Dioptra?

(n.) An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.
Webster's Revised Unabridged Dictionary
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APAWebster's. (2011). dioptra. Retrieved September 21, 2026, from http://smartdefine.org/dioptra/definitions/1997846
ChicagoWebster's. 2011. "dioptra" http://smartdefine.org/dioptra/definitions/1997846 (accessed September 21, 2026).
HarvardWebster's 2011, dioptra, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/dioptra/definitions/1997846>.
MLAWebster's. "dioptra" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/dioptra/definitions/1997846>