Paul is quite correct.
Maximillian Schuler was a German naval engineer who was involved in engineering theory and experiments as to how to keep a ship's gimballed compass (the ancient brass and heavy systems that were used from about the beginning of the eighteenth century) level despite rolling and pitching movements of the ship. He reasoned that if the compass suspension system was hooked to a pendulum (mass not calculated) the mass of which was placed at the centre of the mass of the earth, then the gimbal and compass system would remain level. Unfortunately it proved impossible to place a pendulum mass at the centre of the earth! Still, 2pie root l/g is about 84.4 minutes at earth average radius. Modern Schuler frequency curves account for distance above earth surface using, normally, baro-inertial height loops
Happy new year, David