The instrument consists of two - round scales. One with index and the other with vernier. The first scale (index scale) is for tuning the analyser into the azymuth. The Second scale (Vernier Scale). The Wedge Box contains two wedges cut in mutually perpendicular direction of optics axis in quartz. The long wedge is movable by means of a micrometer drum, with the help of which accurate reading of the movement is taken. Micrometer screw minimum reading 0.001cm. (i.e. is for measuring the degree of
orientation of a wedge box.