How come GPS reads different

Its a 296. It seems the like the higher I go the farther off it is.
I am one to think the GPS would be more accurate than the altimeter.
I was thinking that we get incorrect altimeter settings
"Casey Wilson" N2310D @ gmail.com wrote in message
news:x1Pqe.2896$9a1.185@trnddc01...

"Aluckyguess" wrote in message
...
I am getting over 500ft. difference and more.
"Matt Whiting" wrote in message
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Aluckyguess wrote:
How come the GPS reads a different altitude than the Altimeter?

For many reasons. The main reason is that they derive altitude by two
completely different methods and this inevitably introduces errors. Then
each method has its own inherent errors.

Even two altimeters side by side won't read the same altitude other than
by accident.


Matt

The number of sattelites being received is one of the variables -- how
many are you registering on the GPS? What brand/model is the GPS. Is the
GPS certified for navigation? Does the GPS have a Kohlsman equivalent
input? What are the altitude specifications of the GPS? Are you comparing
it to an altimeter in an airplane? Is the calibration data on the
altimeter valid? Have you compared the altimeter to the GPS while parked
at a known reference (i.e., the benchmark of your local airport)? My
Magellan handheld takes about five mintues of averaging to get a
reasonably close altitude correlation -- how much time are you giving
yours?

Bottom line, forget the GPS altitude reading, dial in the local pressure
data into the airplane's altimeter and trust it.