Year	mm Hg
1980	135.9
1981	135.9
1982	135.9
1983	135.9
1984	135.9
1985	135.8
1986	135.7
1987	135.6
1988	135.4
1989	135.2
1990	134.9
1991	134.5
1992	134
1993	133.4
1994	133
1995	132.6
1996	132.3
1997	132.1
1998	132
1999	131.9
2000	132
2001	132.1
2002	132.2
2003	132.4
2004	132.6
2005	132.9
2006	133.1
2007	133.5
2008	133.8