Ron Lee writes:

With SA off the vertical error is probably better that altimeter
accuracy requirements.

No. The figure of hundreds of feet is with SA OFF. It's even worse
with SA on.

At least close enough for most users and if
you can get WAAS corrections it is very good.

If you have external corrections, you can do far better. But you're
still at least as well off with a standard altimeter. At least right
now, you don't really gain anything for altitude measurement with GPS.

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