double sextant

double sextant

[¦dəb·əl ′sek·stənt] (navigation) A sextant designed to enable the observer to measure simultaneously the left and right horizontal sextant angles of a three-point problem; this sextant differs from a standard sextant in that it comprises a circle with two indices inscribed and two coaxial index mirrors; the horizon glass is silvered top and bottom but is clear in the middle to permit direct observation of the center object ashore.