Year	mm Hg
1980	139.7
1981	139.6
1982	139.5
1983	139.4
1984	139.3
1985	139.1
1986	138.9
1987	138.7
1988	138.5
1989	138.2
1990	137.9
1991	137.6
1992	137.1
1993	136.7
1994	136.3
1995	135.9
1996	135.6
1997	135.3
1998	135.2
1999	135.1
2000	135.2
2001	135.2
2002	135.4
2003	135.6
2004	135.9
2005	136.2
2006	136.5
2007	136.9
2008	137.2