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. Perhaps
the problem has something to do with the partially "squished" globe that the
earth actually is? TTYL


> My understanding of it is that the GPS system gives an altitude above a
> "fake" globe, which may or may not exactly match the "real" globe, which
> isn't perfect and has bumps and bulges... (GRIN)...
>
> Nate
>
> On Wed, 2002-09-04 at 18:48, Herbert Graf wrote:
> > Excuse my ignorance but what is a "datum"? FWIW I have checked
> the altitude
> > reading I get from my GPS in several places and as far as I can
> tell it's
> > pretty darn accurate, I'd say to about 10 meters, more then
> enough for many
> > cases. TTYL
> >
> > > GPS altitude is measured above a "datum" and sometimes is accurate,
> > > sometimes not...

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