Year	Measure
1800	882.5
1820	886.7
1913	1521
1950	3801
1951	4262
1952	4087
1953	3926
1954	4552
1955	4993
1956	5208
1957	5385
1958	5543
1959	6073
1960	6291
1961	6741
1962	7106
1963	7546
1964	7982
1965	8462
1966	8351
1967	8394
1968	9489
1969	10420
1970	10930
1971	11750
1972	12790
1973	13010
1974	13530
1975	13690
1976	13590
1977	13310
1978	13660
1979	14190
1980	14820
1981	15320
1982	15370
1983	15630
1984	15460
1985	15720
1986	16230
1987	17120
1988	17190
1989	17050
1990	17500
1991	17540
1992	18050
1993	18200
1994	19300
1995	20150
1996	20640
1997	20900
1998	21110
1999	21330
2000	22830
2001	22380
2002	21910
2003	22090
2004	22930
2005	23850
2006	24670
2007	25560
2008	26040
2009	25760
2010	26460
2011	27080
2012	27320
2013	27690
2014	28160
2015	28540
2016	28900
2017	29240
2018	29600