Year	mm Hg
1980	138.5
1981	138
1982	137.6
1983	137.2
1984	136.7
1985	136.3
1986	135.9
1987	135.6
1988	135.3
1989	134.9
1990	134.6
1991	134.3
1992	134
1993	133.7
1994	133.6
1995	133.5
1996	133.5
1997	133.6
1998	133.8
1999	134
2000	134.3
2001	134.6
2002	135
2003	135.3
2004	135.7
2005	136.1
2006	136.6
2007	137.1
2008	137.5