Recently, Ben Jackson posted:

More precisely it's showing the height above the datum, which is the
mathematical model of the earth ellipsoid the GPS uses to approximate
the actual Earth.


"Neil Gould" wrote in message
k.net...

General question: is there are practical difference between the datum and
MSL? Neither have any local relevance, AFAICT.

The geoid height is typically -100 ft over the US, meaning that the zero of
the NAD 83 ellipsoid and mean sea level differ by about 100 ft.

Julian Scarfe