Year	Measure
1800	876.8
1820	876.8
1913	1185
1970	26850
1971	25880
1972	28490
1973	34010
1974	48720
1975	50930
1976	37130
1977	35390
1978	35740
1979	32290
1980	17340
1981	15310
1982	15500
1983	14960
1984	14930
1985	13250
1986	12920
1987	12550
1988	14940
1989	15270
1990	15990
1991	15020
1992	13700
1993	11690
1994	12200
1995	13160
1996	14130
1997	14060
1998	13970
1999	12920
2000	12720
2001	12710
2002	12130
2003	11890
2004	12400
2005	13010
2006	13330
2007	13540
2008	13330
2009	13640
2010	13830
2011	13980