Signedengraved on base of protractor: KEUFFEL & ESSER Co / NEW YORK
FunctionThe purpose of crystallographic goniometry is to measure the interfacial angles of crystals to determine their type.
To determine the angle between two surfaces, one has to hold the crystal edge at the scissor opening between the diameter and the moving arm. The angular vernier scale permits high accuracy measurements of the angle.
ProvenanceProf. Clifford Frondel, Geology, Harvard University