Year	mm Hg
1980	138.8
1981	138.5
1982	138.1
1983	137.9
1984	137.6
1985	137.3
1986	137
1987	136.7
1988	136.4
1989	136.2
1990	136
1991	135.8
1992	135.6
1993	135.3
1994	135
1995	134.6
1996	134.3
1997	134
1998	133.7
1999	133.3
2000	133
2001	132.6
2002	132.3
2003	132
2004	131.6
2005	131.3
2006	131
2007	130.7
2008	130.4