Principle
As first explained by German engineer Maximilian Schuler in a 1923 paper, a pendulum whose period exactly equals the orbital period of a hypothetical satellite orbiting just above the surface of the Earth (about 84 minutes) will tend to remain pointing at the center of the Earth when its support is suddenly displaced. Such a pendulum would have a length equal to the radius of the Earth. Consider a simple gravity pendulum, whose length equals the radius of the Earth, suspended in a uniform gravitational field of the same strength as that experienced at the Earth's surface. If suspended from the surface of the Earth, the bob of the pendulum would be at the center of the Earth. If it is hanging motionless and its support is moved sideways, the bob tends to remain motionless, so the pendulum always points at the center of the Earth. If such a pendulum were attached to the inertial platform of an inertial navigation system, the platform would remain level, facing "north", "east" and "down", as it was moved about on the surface of the Earth.
A rigid pendulum may also be made to have the required period, with a pivot near its center of gravity.
The Schuler period can be derived from the classic formula for the period of a pendulum:
where L is the radius of the earth in meters and g is the local acceleration of gravity in metres per second per second.
Read more about this topic: Schuler Tuning
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