Year	Measure
1800	1409
1820	1409
1913	2600
1938	6290
1950	6290
1960	13690
1961	14400
1962	15120
1963	15880
1964	16710
1965	17610
1966	18380
1967	19320
1968	20150
1969	21220
1970	19420
1971	19230
1972	18150
1973	19140
1974	15630
1975	13060
1976	13460
1977	14380
1978	16070
1979	19830
1980	20670
1981	19640
1982	20430
1983	21360
1984	21420
1985	21870
1986	22020
1987	22440
1988	22550
1989	22670
1990	21910
1991	20600
1992	19430
1993	19120
1994	19350
1995	19840
1996	20330
1997	20990
1998	22070
1999	22620
2000	22730
2001	22600
2002	22810
2003	22740
2004	22750
2005	23020
2006	23310
2007	23370
2008	22560
2009	21220
2010	21020
2011	21130
2012	21420
2013	21750
2014	22050
2015	22350
2016	22660
2017	22970
2018	23280