Year	mm Hg
1980	140.8
1981	140.7
1982	140.6
1983	140.4
1984	140.2
1985	140
1986	139.8
1987	139.6
1988	139.4
1989	139.3
1990	139.1
1991	139
1992	138.8
1993	138.5
1994	138.2
1995	137.9
1996	137.6
1997	137.4
1998	137.2
1999	137.3
2000	137.3
2001	137.3
2002	137.5
2003	137.7
2004	137.9
2005	138.1
2006	138.3
2007	138.4
2008	138.6