2 in box sextant in bronzed brass with pin-hole plane sight reading to 1 minute of arc.
A box sextant is used for observing and setting out angles up to 120°. In principle it is the same as an optical square except that the user can adjust the angle by rotating one of the mirrors. The instrument can be fitted with a small telescope for long distance sightings.
Used for measuring horizontal angles often in conjunction with ranging rods where the accuracy of a theodolite is not required.