The two ways to express altitude are described below.
This is the difference in the altitudes between two locations.
Example: Height measured from the ground to the top of a building ()
Sea Level Altitude (Elevation):
Altitude measured from sea level.
Example: Height measured from sea level to the top of a building ()
The altitude readings produced by your watch are relative altitudes, based on the fact that barometric pressure drops as altitude increases. The altitude values displayed by your watch are based on International Standard Atmosphere (ISA) relative altitude data defined by the International Civil Aviation Organization (ICAO).