Conventional International Origin (CIO) is a conventionally defined reference axis of the pole's average location on the Earth's surface over the year 1900–1905.
[1] Polar motion is the movement of Earth's rotation axis across its surface.
The axis of the Earth's rotation tends, as the axis of a gyroscope, to maintain its orientation to inertial space.
The Conventional International Origin is used to measure this movement.
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