Schuler pendulum

Schuler pendulum

[′shü·lər ‚pen·jə·ləm]
(mechanics)
Any apparatus which swings, because of gravity, with a natural period of 84.4 minutes, that is, with the same period as a hypothetical simple pendulum whose length is the earth's radius; the pendulum arm remains vertical despite any motion of its pivot, and the apparatus is therefore useful in navigation.