Before revision: Starting in the late twentieth century, improved measurements of satellite orbits and star positions have provided extremely accurate determinations of the earth 's center of mass and of its axis of revolution; and those parameters have been adopted also for all modern reference ellipsoids.
After revision: Starting in the late twentieth century, improved measurements of satellite orbits and star positions have provided extremely accurate determinations of the Earth 's center of mass and of its axis of revolution; and those parameters have been adopted also for all modern reference ellipsoids.