Year	mm Hg
1980	138
1981	138
1982	138.1
1983	138.1
1984	138.1
1985	138
1986	137.9
1987	137.9
1988	137.8
1989	137.8
1990	137.7
1991	137.5
1992	137.2
1993	136.9
1994	136.6
1995	136.3
1996	136.1
1997	135.9
1998	135.8
1999	135.7
2000	135.6
2001	135.6
2002	135.6
2003	135.5
2004	135.5
2005	135.5
2006	135.5
2007	135.5
2008	135.5