Year	mm Hg
1980	136.1
1981	136
1982	135.8
1983	135.7
1984	135.5
1985	135.4
1986	135.2
1987	135
1988	134.8
1989	134.6
1990	134.4
1991	134.1
1992	133.8
1993	133.5
1994	133.1
1995	132.6
1996	132.3
1997	131.9
1998	131.7
1999	131.4
2000	131.3
2001	131.3
2002	131.3
2003	131.3
2004	131.4
2005	131.4
2006	131.5
2007	131.5
2008	131.5