"Travis Marlatte" wrote:

Regardless, in this case GPS derived altitude was quite good.

Ron Lee

One of the challenges with GPS fixes (both horizontal and vertical) is that
there is a statistical distribution of the error. Most receivers advertise
being within 15' laterally, 90% of the time. It's that other 10% that you
gotta worry about.

Surveyors improve their accuracy by leaving the GPS receiver stationary to
get a statistical sampling that can reveal the true position.

Travis

Correct point Travis but since I fly VFR I use other references to
develop a "blended" solution. Plus my primary GPS receiver has
integrity to catch the really bad errors (rare).

Ron Lee