Year	2011 U.S. Dollars
1970-01-01	24.84
1971-01-01	25.71
1972-01-01	27.51
1973-01-01	29.31
1974-01-01	30.53
1975-01-01	30.68
1976-01-01	32.51
1977-01-01	33.28
1978-01-01	34.49
1979-01-01	35.24
1980-01-01	37.24
1981-01-01	38.35
1982-01-01	39.42
1983-01-01	39.93
1984-01-01	40.34
1985-01-01	40.67
1986-01-01	41.64
1987-01-01	42.67
1988-01-01	44.16
1989-01-01	45.24
1990-01-01	45.77
1991-01-01	47.51
1992-01-01	49.00
1993-01-01	50.23
1994-01-01	52.07
1995-01-01	51.56
1996-01-01	53.03
1997-01-01	54.17
1998-01-01	53.90
1999-01-01	54.94
2000-01-01	57.14
2001-01-01	55.67
2002-01-01	56.40
2003-01-01	57.09
2004-01-01	59.32
2005-01-01	58.91
2006-01-01	59.79
2007-01-01	60.78
2008-01-01	59.98
2009-01-01	59.07
2010-01-01	59.86
2011-01-01	60.17