Gyroscope is a device used for measuring/maintaining orientation, based on the principle of conservation of angular momentum and have been used in the airplanes, space satelites and missiles (in their inertial navigation and attitude control systems).

Among various kinds of gyroscopes, the one of the most accurate is the Fiber Optic Gyroscope (FOG), which is a coil of as much as 5 km of optical fiber and uses the interference of light to detect mechanical rotation (exploiting Sagnac effect). FOG provides extremely precise rotational rate information, due to its lack of cross-axis sensitivity to vibration, acceleration, and shock. Moreover, the FOG has virtually no moving parts and no inertial resistance to movement.