Year	US Dollars adjusted for inflation)
1980	19.24
1981	19.31
1982	19.36
1983	19.53
1984	20.13
1985	20.25
1986	20.62
1987	20.96
1988	20.88
1989	21.08
1990	21.22
1991	21.5
1992	21.98
1993	22.49
1994	23.02
1995	23.47
1996	23.87
1997	24.68
1998	25.21
1999	25.67
2000	26.51
2001	26.65
2002	27.54
2003	28.42
2004	29.35
2005	30
2006	30.82