Qualitative studies of the optical properties of crystals under the polarizing microscope and refractive index measurements by immersion methods are made on slides placed upon the microscope stage. These procedures have the disadvantage that the crystals have a fixed orientation. Quantitative properties, such as optic axial angles, are measured on an accessory to the microscope, such as the universal stage, which although allowing rotation of the crystal necessitates auxiliary stereographic projection and is often considered laborious in operation and is not widely employed.