You can't calibrate the sensor to both altitude and atmospheric pressure. You set either the pressure and the sensor tells you your elevation, or you tell the watch your elevation and it will tell you the atmospheric pressure.
Tech support suggested the latter for a more accurate reading.
Also they said that if you are setting the pressure and expecting a measurement of your exact elevation - specs say it should be within 200 feet. (Mine was out by a hundred and 70), as good as it gets I guess.
