Year	US Dollars adjusted for inflation)
1980	16.37
1981	16.35
1982	16.25
1983	15.76
1984	16.19
1985	16.15
1986	16.73
1987	17.18
1988	17.58
1989	17.95
1990	18.25
1991	18.18
1992	17.41
1993	17.99
1994	18.63
1995	17.91
1996	18.47
1997	19.6
1998	20.16
1999	19.62
2000	19.97
2001	20.75
2002	21.4
2003	22.01
2004	23.77
2005	24.85
2006	24.29