For elevations or altitudes, often just the abbreviation MSL is used, e.g.,Mount Everest (8849 m MSL), or the reference to sea level is omitted completely, e.g., Mount Everest (8849 m).[7]
Pressure altimeter measuringatmospheric pressure, which decreases as altitude increases. Since atmospheric pressure varies with the weather, too, a recent local measure of the pressure at a known altitude is needed to calibrate the altimeter.
Accurate measurement of historical mean sea levels is complex. Land masssubsidence (as occurs naturally in some regions) can give the appearance ofrising sea levels. Conversely, markings on land masses that areuplifted (due to geological processes) can suggest a relative lowering of mean sea level.[10]
^"TOWAIR Determination". Federal Communications Commission. Retrieved3 February 2024.Site Elevation (AMSL) – The elevation of the site above mean sea level (AMSL).
^"General Concepts". Los Angeles Air Route Traffic Control Center. Retrieved6 April 2024.Sometimes, you will still see the abbreviation 'ASL' used as well; it stands for 'Above Sea Level'.
^abNegrini, Robert M.; et al. (July 2006). "The Rambla highstand shoreline and the Holocene lake-level history of Tulare Lake, California, USA".Quaternary Science Reviews.25 (13):1599–1618.Bibcode:2006QSRv...25.1599N.doi:10.1016/j.quascirev.2005.11.014.elevations from 210 fasl (64 masl) to 230 fasl (70 masl) on the Kettleman City 7.5' USGS topographic map
^Church, J. A.; Clark, P. U. (2013)."Chapter 13: Sea Level Change"(PDF).Climate Change 2013: The Physical Science Basis. Cambridge University Press. pp. 1137–1216. Retrieved20 April 2024.
