http://wikiless.i2p/wiki/Sea_level?lang=en
The term APSL means above present sea level, comparing sea levels in the past with the level today. Earth's radius at sea level is 6,378.137 km (3,963.191 mi) at the equator. It is 6,356.752 km (3,949.903 mi) at the poles and 6,371.001 km (3,958.756 mi) on average. [ 2 ] This flattened spheroid , combined with local gravity anomalies , defines the geoid of the Earth, which approximates the local mean sea level for locations in the open ocean.