Abstract: Fiber-optic gyroscope （FOG） can be used to measure the velocity of rotation on its axis. Using this method and four-position scheme, we measure the north of the earth, the latitude of laboratory and the speed of self-rotation of the earth. The main principles of FOG north seeker and four-position scheme are introduced. The experimental equipment of north seeker, experimental steps and the data treatment method are also discussed.

Key words: FOG： four-position scheme, two-axis turntable, north seeker