Year	mm Hg
1980	134.8
1981	135
1982	135.2
1983	135.3
1984	135.5
1985	135.6
1986	135.7
1987	135.7
1988	135.6
1989	135.5
1990	135.3
1991	135.1
1992	134.8
1993	134.4
1994	134.1
1995	133.8
1996	133.6
1997	133.4
1998	133.2
1999	133
2000	132.9
2001	132.9
2002	132.8
2003	132.9
2004	132.9
2005	133
2006	133.1
2007	133.2
2008	133.4