Year	Measure
1800	775.7
1820	775.7
1913	1431
1970	2819
1971	3026
1972	3183
1973	3312
1974	3494
1975	3590
1976	3821
1977	4080
1978	4406
1979	4841
1980	5268
1981	5355
1982	5296
1983	5271
1984	5850
1985	6266
1986	7057
1987	7742
1988	8513
1989	9209
1990	9422
1991	9410
1992	9630
1993	10120
1994	10500
1995	10730
1996	11280
1997	11900
1998	11860
1999	12130
2000	12490
2001	12570
2002	12540
2003	12440
2004	13220
2005	13680
2006	14030
2007	14420
2008	14700
2009	13800
2010	13540
2011	13020
2012	12660
2013	12650
2014	12800
2015	12960
2016	13140
2017	13330
2018	13520