Year	mm Hg
1980	139
1981	139.2
1982	139.3
1983	139.4
1984	139.5
1985	139.5
1986	139.6
1987	139.6
1988	139.6
1989	139.5
1990	139.4
1991	139.2
1992	138.9
1993	138.4
1994	138.1
1995	137.7
1996	137.4
1997	137.2
1998	137
1999	136.8
2000	136.8
2001	136.8
2002	136.8
2003	136.9
2004	136.9
2005	137
2006	137
2007	137
2008	136.9