endless tangent screw sextant

endless tangent screw sextant

[′end·ləs ′tan·jənt ‚skrü ′sek·stənt]
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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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.