That doesn't sound right. The reason a calibration is necessary after switching batteries is because of the lack of memory retention without power. I'll have to recheck my manual to verify your statement. [Note: Mine says to recalibrate after moving long distances, large temperature changes or battery changes. To what degree is goes out of calibration I don't know but I suspect it is much less that what people think.]

The barometer/altimeter can be set to known air pressure levels but that's a hassle unless you have an accurate barometer to compare it to. That makes it superior to the gps signal. I use the gps signal to give me the altitude because it is more convenient. Remember though that with the gps signal, the vertical component of the unit is subject to 1/4x the accuracy of the horizontal component. A 3 metre horizontial accuracy equates to a max of 12 metre vertical accuracy. That's probably one reason why people have doubted it's usability.

Between models, even with the same manufacturer the accuracy may vary. The barometer on my 62s indicates an elevation at least 15 less than my 60CSx and this is borne out in real life comparisons to benchmarks. My 62s autocalibrates the altimeter on every turn on. It can be set to record air pressure only when on or alternately even when off at some battery expense.