Year	mm Hg
1980	136.4
1981	136.5
1982	136.5
1983	136.5
1984	136.5
1985	136.5
1986	136.4
1987	136.3
1988	136.3
1989	136.2
1990	136.1
1991	135.9
1992	135.7
1993	135.5
1994	135.2
1995	134.9
1996	134.5
1997	134.3
1998	134
1999	133.9
2000	133.8
2001	133.7
2002	133.6
2003	133.6
2004	133.6
2005	133.6
2006	133.6
2007	133.6
2008	133.7