Figure 2

Schematic of the calibrating northern direction using the North Star.
A high-precision encoder is on the rotary platform, and the platform heading can be defined using the encoder. There is a mirror (Mirror 2) in our laboratory whose vertical direction is calibrated using the North Star. The vertical direction of the mirror plane is the north direction. A laser beam is parallel to the co-magnetometer x-axis to be incident on Mirror 2, as the reflected beam is coincident with the input beam. The heading degree on the encoder is the north direction.