EBBCO Sextant in plastic box. Used in land surveying for measuring horizontal angles often in conjunction with ranging rods where the accuracy of a theodolite is not required. This is a marine sextant and was presumably used for land surveying by the donor. There is a User Guide entitled “The EBBCO Sextant Its Use, Care and Adjustment” by JGP Weatherlake MRIN.
Ebbco began making these plastic sextants in the 1960’s especially as a navigational aid for yachtsmen. They were designed and manufactured to satisfy the less expensive end of the market.