Altimeter Setting
The altimeter pressure setting is based on a standard atmosphere with the station pressure reduced to sea level and is derived similarly to the sea level pressure. It plays an important role in aviation operations. Essentially, the altimeter needs to be manually set to the appropriate sea level pressure for that location so it can report a correct altitude value (in feet).
On a ship, the altimeter setting can be calculated to the height of the flight deck. Ships operating in the same area can therefore have different altimeter settings. You can obtain an altimeter setting based on elevation above sea level using various online calculators.
On the flight deck, the plane's altimeter will report the altitude (above mean sea level).