sextant- ¹ The sixth part of a circle. ² A double-reflecting instrument for measuring altitudes of celestial bodies from a moving ship or airplane. Originally, the term was applied only to instruments with an arc of 60° (a range of 120°); very few similar, modern instruments are sextants in the original sense.

sextant, bubble—A sextant in which the bubble of a spirit level serves as the horizon.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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