Schuler tuning is a design principle for inertial navigation systems that accounts for the curvature of the Earth.
An inertial navigation system, used in submarines, ships, aircraft, and other vehicles to keep track of position, determines directions with respect to three axes pointing "north", "east", and "down".
As first explained by German engineer Maximilian Schuler in a 1923 paper,[1] a pendulum that has a period that equals the orbital period of a hypothetical satellite orbiting at the surface of Earth (about 84.4 minutes) will tend to remain pointing at the center of Earth when its support is suddenly displaced.
The inertial platform is mounted on gimbals, and an electronic control system keeps it pointed in a constant direction with respect to the three axes.
As the vehicle moves, the gyroscopes detect changes in orientation, and a feedback loop applies signals to torquers to rotate the platform on its gimbals to keep it pointed along the axes.
An inertial navigation system is tuned by letting it sit motionless for one Schuler period.