Year	US Dollars adjusted for inflation)
1980	20.15
1981	20.34
1982	20.47
1983	20.79
1984	21.96
1985	22.16
1986	22.66
1987	23.38
1988	23.79
1989	24.35
1990	24.46
1991	24.46
1992	25.4
1993	25.77
1994	26.81
1995	27.61
1996	27.63
1997	28
1998	28.16
1999	28.44
2000	29.22
2001	29.22
2002	29.02
2003	28.68
2004	28.89
2005	29
2006	29.28