Year	mm Hg
1980	137.1
1981	137.2
1982	137.2
1983	137.2
1984	137.2
1985	137.1
1986	137.1
1987	137
1988	137
1989	136.9
1990	136.7
1991	136.5
1992	136.2
1993	135.8
1994	135.4
1995	135
1996	134.9
1997	134.7
1998	134.6
1999	134.6
2000	134.6
2001	134.8
2002	134.9
2003	135
2004	135.1
2005	135.2
2006	135.3
2007	135.4
2008	135.4