Herbert Graf <mailinglist@FARCITE.NET> wrote:
> I still don't understand. While the earth has bumps they don't matter,
> altitude is based on sea level, sea level doesn't have bumps, AFAIK.

Actually, it does, even ignoring the effects of tides and weather.
The density of the earth is far from constant, and the "geoid" -- the
equipotential gravitational surface that corresponds to mean sea level --
is quite lumpy indeed.

-- Dave Tweed

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