Do those amounts vary with location? How large a difference is there between
the 2? I remember reading about the 2 standards, but forget how the mean
geoid is determined.

But you're right. If that's true, and I don't doubt it is, GPS would be
better suited to terrain avoidance and less so to aircraft separation.

mike

"Mxsmanic" wrote in message
...
mike regish writes:

My point is that they both are, basically, the same frame of
reference-height above sea level.

Nope. GPS is height above the mean surface of the geoid, altimeter is
height above mean sea level. They can be hundreds of feet apart.

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