O8
I completely agree with you conclusions the altimeter will rarely display true altitude. Indeed this is the point I was trying to make. There seemed to be some suggestion in this thread and previous threads that the altimeter would take temperature into consideration and correct this error. As you point out that is not the case.
Just to reinforce this. To use your example, in each case the pressure acting on the altimeter capsule will be 26.82in Hg and the altimeter will indicate 3000 ft. As you point out this will only be the true altitude on the standard day. But 26.82in Hg = 3000 ft period. The altimeter will not attempt to correct for true altitude by taking temperature into account, that is up to you the pilot (or anyone else who maybe interested.)
What the altimeter will try and do is ensure that 26.82 ALWAYS equals 3000ft regardless of the temperature. For example in the Artic the lower temperature makes the capsule become more elastic and it will expand slightly more than it would do normally, even though it has the same pressure acting on it. If uncorrected this would cause the altimeter to overead. But at the same time a bi-metallic spring acting on the capsule slightly increases its force to compensate, so the net movement is the same as it was in standard conditions.
As Long Range Cruise has pointed out an altimeter is nothing more than an aneroid barometer (except that is calibrated to display altitude instead of pressure)
Max
[ 15 February 2002: Message edited by: max motor ]</p>