When manually calibrating altimeter using GPS it normally suggest a pretty accurate height the first seconds, however, when I start an activity with the barometer set on automatic the calibration is often far off. In my opinion manual and automatic calibration via GPS should yield the same results. A bit more sophisticad case logic in the automatic algorithm perhaps? :)
Further, I've currently been "54 m under water" for quite a while, including sleep at 14 m below sea level last night. A bit weird as I calibrated my watch inserting the correct height manually yesterday evening. Perhaps the above mentioned fix could solve some "underwater-problems" as well?
I have formerly had issues when my watch was stuck at 256 m below sea level after driving through a underwater tunnel. The solution then was to perform a hard reset, customer service also told me that an update for the altimeter algorithm was in beta testing.