Analysis model of optical path difference in Michelson interference

In Michelson interferometer,the actual mirror and the virtual mirror may not be absolutely parallel,an analysis model of the optical path difference in Michelson interference was established,and the optical path difference formula was deduced,which can be used to calculate accurately the the optical path difference in equal inclination interference and equal thickness interference.Equal inclination interference,equal thick interference,and their relationship were perfectly described.