Year	mm Hg
1980	138.2
1981	138.4
1982	138.6
1983	138.8
1984	138.9
1985	139
1986	139
1987	139.1
1988	139.1
1989	139
1990	138.8
1991	138.5
1992	138.2
1993	137.9
1994	137.6
1995	137.3
1996	137.1
1997	136.8
1998	136.6
1999	136.5
2000	136.4
2001	136.3
2002	136.3
2003	136.2
2004	136.2
2005	136.2
2006	136.1
2007	136.1
2008	136.1