Year	Measure
1800	629.4
1820	629.4
1913	972.4
1950	4584
1951	4839
1952	4913
1953	4996
1954	5211
1955	5188
1956	5136
1957	5240
1958	5273
1959	5403
1960	5673
1961	5216
1962	5527
1963	5893
1964	5965
1965	5836
1966	5836
1967	5708
1968	6045
1969	5886
1970	6161
1971	6975
1972	7222
1973	7728
1974	7679
1975	7793
1976	8406
1977	8847
1978	9313
1979	10690
1980	10250
1981	9381
1982	9094
1983	8858
1984	9106
1985	9867
1986	9978
1987	10390
1988	10750
1989	11280
1990	11950
1991	12140
1992	12850
1993	13560
1994	13130
1995	13080
1996	14290
1997	15920
1998	16740
1999	16160
2000	15230
2001	14830
2002	14930
2003	14000
2004	13520
2005	14200
2006	15220
2007	16670
2008	15990
2009	15910
2010	16340
2011	16970
2012	17240
2013	17590
2014	18070
2015	18540
2016	19000
2017	19460
2018	19920