Conventional International Origin
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.
- Muneendra Kumar (2007). "Coordinates : A resource on positioning, navigation and beyond - Blog Archive - The Real Definition of ITRF". mycoordinates.org. Retrieved 2014-05-22.