"smf" wrote in message =
news:jpblc.12364$bS1.6242@okepread02...
My Altimeter is accurate when on the ground or at lower alt. When I =
climb up
to 7k and above and check it against GPS and approach controls read =
out it
is about 300+ feet off.
=20
Is it the altimeter I'm having problems with?
=20
Steve
=20
It's possible you are not having any problems at all.
Barometric altimetry simply does not measure geometric height.
And most GPSs ignore barometric settings completely.

I'm unsure what you mean by "approach controls read out".
The controller can see only what your Mode C transponder sends.
Usually that reading is to the nearest 100 feet, and it derives from
a barometric sensor in your airplane, permanently set to 29.92 in.hg.

With a correct barometric setting, your altimeter should show the =
relevant
airport's elevation at its true height, but normally *not* any other =
elevation.
If your altimeter passes its 24-month 91.411 check, it's surely OK.
If it fails its check, though, you do have an altimeter problem.
---JRC---