
Originally Posted by
Expatio
Calibrate?
Why would it need to calibrated.
A pressure altimeter (barometer altimeter) as found on aircraft is set by user before each journey. As non pilots; we would not have access to QNH (pressure at sea level) data on a daily/hourly basis, so we set our altimeters' altitude instead.
So say your house was at 150' above sea level; before your journey, you would set the altitude at 150'. As the barometer reads the air pressure, it adjusts the altitude reading (as we accend, the air pressure decreases and the altitude reading increases). If we went down to sea level it air pressure increasse and would give a reading of zero feet (MSL).