Year	mm Hg
1980	138.1
1981	137.7
1982	137.4
1983	137
1984	136.6
1985	136.2
1986	135.9
1987	135.8
1988	135.7
1989	135.6
1990	135.6
1991	135.6
1992	135.6
1993	135.5
1994	135.5
1995	135.5
1996	135.4
1997	135.4
1998	135.3
1999	135.3
2000	135.2
2001	135.2
2002	135.1
2003	135.1
2004	135
2005	134.8
2006	134.8
2007	134.7
2008	134.6