Year	mm Hg
1980	138
1981	138
1982	138
1983	137.9
1984	137.8
1985	137.7
1986	137.5
1987	137.4
1988	137.2
1989	137.1
1990	136.9
1991	136.7
1992	136.5
1993	136.2
1994	135.9
1995	135.6
1996	135.4
1997	135.2
1998	135.1
1999	135.1
2000	135.1
2001	135.2
2002	135.4
2003	135.6
2004	135.8
2005	136
2006	136.2
2007	136.4
2008	136.6