Year	mm Hg
1980	137
1981	136.9
1982	136.8
1983	136.7
1984	136.6
1985	136.5
1986	136.4
1987	136.2
1988	136
1989	135.9
1990	135.7
1991	135.4
1992	135.1
1993	134.7
1994	134.2
1995	133.7
1996	133.4
1997	133
1998	133
1999	133.1
2000	133.2
2001	133.4
2002	133.5
2003	133.7
2004	133.8
2005	134
2006	134.1
2007	134.2
2008	134.3