radius 16 inches
This octant clearly dates from the late eighteenth century. It has a
mahogany frame and index arm. The boxwood scale is graduated every 20 minutes from 0o to 90o and read by transversals to 2 minutes of arc. The top of the scale is numbered counterclockwise for zenith distances. There is also a back sight and a back horizon glass that can be used to measure angles greater than 90o.