Year	mm Hg
1980	143.1
1981	142.5
1982	141.9
1983	141.2
1984	140.6
1985	140.1
1986	139.6
1987	139.2
1988	138.9
1989	138.6
1990	138.3
1991	137.9
1992	137.5
1993	137.1
1994	136.7
1995	136.3
1996	136
1997	135.6
1998	135.4
1999	135.1
2000	134.9
2001	134.8
2002	134.8
2003	134.8
2004	134.8
2005	134.9
2006	135
2007	135.2
2008	135.3