Abstract: The fiber-optic gyroscope （FOG） can be used to measure the size of its axial velocity. Using this sensitivity, we measure the north of the earth and the latitude of laboratory. The experiments of FOG north seeker are introduced briefly. The article focuses on two different definitions of latitude and analyze calculation results. We also discuss the relationship between the method of current international common calculating latitude and the Chinese general method, and give the conversion between them.

Key words: fiber-optic gyroscope, finding north, Sagnac effect, latitude