Year	US Dollars adjusted for inflation)
1980	21.18
1981	21.25
1982	20.97
1983	21.25
1984	21.91
1985	22.3
1986	22.27
1987	21.9
1988	22.02
1989	22.57
1990	22.82
1991	22.26
1992	22.61
1993	22.72
1994	22.89
1995	23.33
1996	23.52
1997	24.05
1998	24.35
1999	24.16
2000	24.86
2001	25.29
2002	25.52
2003	25.37
2004	25.93
2005	26.42
2006	26.57