In practice, the direction of vibration of the upper and lower polarising mirrors of the polarising microscope should be orthogonal to each other, or in the east-west and north-south directions, each being in line with the cross filament of the eyepiece in both the transverse and longitudinal directions. Sometimes only one lower polariser is used for observation, and the direction of vibration of the lower polariser must be determined, so the polariser must be corrected during operation.

(1) Inspection of the eyepiece cross filament
Generally check whether the eyepiece cross filament is orthogonal, and whether it is consistent with the direction of vibration of the upper and lower polarizers, and at the same time, select a piece of black mica with a complete resolution pole, move it to the centre of the eyepiece cross filament, place the resolution slit parallel to one of the cross filaments and note down the number of scales of the carrier table, then turn the animal table so that the resolution slit is parallel to the other cross filament, and note down the number of scales of the carrier table, and the difference of the two scales is 90 degree , which indicates that the cross filaments are orthogonal. The difference between the two scales is 90 degree , indicating that the cross filaments are orthogonal.

(2) Determination and correction of the direction of vibration of the lower polariser

(3) Correction of orthogonality of upper and lower polarizers