Mark, You are quite right in that GPS does not consider what the atmospheric pressure is. GPS altitude uses the geodetic center of the Earth as a datum, then corrects that number to Mean Sea Level for display.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA smw...@md.metrocast.net ____________________________________________ Congratulations! I'm sure you know this already, but keep in mind that GPS altitudes differ from the pressure altitude system that altimeters (and encoders) use. The error grows with altitude. Two GPSs will match pretty well at altitude, but the pressure altitude system that the aviation system works on (and your encoder) is inherently "inaccurate" with respect to reality. But we all use the same system, so it works. I didn't realize this until I had a GPS in the plane and compared it to the altimeter at high altitude and wondered why the difference... Mark Langford ML at N56ML.com website at http://www.N56ML.com -------------------------------------------------------- ------------------------------ _______________________________________________ See KRnet list details at http://www.krnet.org/instructions.html End of KRnet Digest, Vol 354, Issue 30 **************************************
