Year	Measure
1800	575.9
1820	575.9
1913	1062
1970	4224
1971	4568
1972	4940
1973	5344
1974	5786
1975	6270
1976	6804
1977	7390
1978	8026
1979	8702
1980	9410
1981	10130
1982	10870
1983	11670
1984	12590
1985	13680
1986	15020
1987	17670
1988	21250
1989	23850
1990	24320
1991	25170
1992	25120
1993	25280
1994	25830
1995	25360
1996	24970
1997	26480
1998	27960
1999	27960
2000	28710
2001	27880
2002	26470
2003	25780
2004	26970
2005	26760
2006	26420
2007	26650
2008	25350
2009	23370
2010	21870
2011	23660