Definition

(British terminology). A simplified and more robustly constructed version of the marine sextant intended primarily for use in HYDROGRAPHIC SURVEY. It has no SHADES, a wide angle low magnification telescope and is generally graduated in MINUTES of arc. It may be fitted with either a VERNIER or a MICROMETER reading device. Both mirrors are silvered all over to enable angles up to 180° to be measured. Some sounding sextants have a 90° prism attachment which reflects the normal direct LINE OF SIGHT 90° to the left. Called surveying sextant, or hydrographic sextant in U.S. terminology.