Year	mm Hg
1980	137.3
1981	137.1
1982	136.8
1983	136.6
1984	136.3
1985	136.1
1986	135.9
1987	135.7
1988	135.5
1989	135.3
1990	135.1
1991	135
1992	134.8
1993	134.6
1994	134.5
1995	134.3
1996	134.2
1997	134.1
1998	134.1
1999	134.1
2000	134.3
2001	134.4
2002	134.5
2003	134.7
2004	135
2005	135.2
2006	135.5
2007	135.8
2008	136.1