Year	mm Hg
1980	138.3
1981	138.4
1982	138.5
1983	138.5
1984	138.5
1985	138.4
1986	138.4
1987	138.3
1988	138.3
1989	138.2
1990	138.1
1991	137.9
1992	137.6
1993	137.4
1994	137.2
1995	137.1
1996	136.9
1997	136.8
1998	136.6
1999	136.5
2000	136.4
2001	136.4
2002	136.4
2003	136.4
2004	136.4
2005	136.4
2006	136.4
2007	136.4
2008	136.4