Year	Measure
1800	518.7
1820	517.3
1870	761.6
1913	1063
1950	1342
1951	1332
1952	1468
1953	1497
1954	1504
1955	1401
1956	1473
1957	1395
1958	1555
1959	1465
1960	1616
1961	1728
1962	1660
1963	1873
1964	1913
1965	1990
1966	1991
1967	1932
1968	2089
1969	2119
1970	2199
1971	2386
1972	2753
1973	2674
1974	2821
1975	2945
1976	3093
1977	3121
1978	3251
1979	3385
1980	3544
1981	3647
1982	3560
1983	3659
1984	3693
1985	3806
1986	3657
1987	3810
1988	3733
1989	3795
1990	4017
1991	4095
1992	4333
1993	4348
1994	4410
1995	4445
1996	4691
1997	4877
1998	5047
1999	5292
2000	5480
2001	5687
2002	5723
2003	5981
2004	6275
2005	6461
2006	6760
2007	7115
2008	7361
2009	7510
2010	7665
2011	7427
2012	7620
2013	7824
2014	8071
2015	8366
2016	8655
2017	8954
2018	9263