Year	mm Hg
1980	138.5
1981	138.5
1982	138.5
1983	138.6
1984	138.6
1985	138.6
1986	138.5
1987	138.5
1988	138.5
1989	138.4
1990	138.4
1991	138.2
1992	137.8
1993	137.3
1994	136.8
1995	136.3
1996	135.9
1997	135.5
1998	135.2
1999	135
2000	134.9
2001	134.8
2002	134.8
2003	134.8
2004	134.9
2005	135
2006	135.2
2007	135.3
2008	135.4