From AMS Glossary
Revision as of 18:28, 25 April 2012 by Perlwikibot
(Or elevation of ivory point.) The vertical distance above mean sea level of the ivory point (zero point) of a station's mercurial barometer; frequently the same as station elevation.
This term is denoted by the symbol Hz in international usage. The value of atmospheric pressure with reference to this level is termed actual pressure.