Year	mm Hg
1980	139.4
1981	139
1982	138.5
1983	138
1984	137.5
1985	137
1986	136.7
1987	136.4
1988	136.3
1989	136.2
1990	136
1991	136
1992	135.9
1993	135.8
1994	135.7
1995	135.7
1996	135.7
1997	135.8
1998	135.8
1999	135.8
2000	135.8
2001	135.8
2002	135.8
2003	135.7
2004	135.6
2005	135.5
2006	135.3
2007	135.1
2008	134.9