endless tangent screw sextant

endless tangent screw sextant

[′end·ləs ′tan·jənt ‚skrü ′sek·stənt]
(navigation)
A marine sextant having an endless tangent screw for controlling the position of the index arm and the vernier or micrometer drum; the index arm may be moved over the entire arc without resetting, by means of the endless tangent screw.