Year	Measure
1800	447.6
1820	447.6
1913	353.8
1950	322.2
1951	334.8
1952	339.3
1953	346.9
1954	359.6
1955	364.6
1956	372
1957	379.6
1958	383.4
1959	398.3
1960	396.9
1961	333.3
1962	355.2
1963	364.1
1964	376.1
1965	380.1
1966	387.5
1967	413
1968	400
1969	388.1
1970	483.3
1971	510.5
1972	464.1
1973	496.1
1974	484.5
1975	478.6
1976	506.2
1977	556.1
1978	536.6
1979	522
1980	539.9
1981	574.5
1982	559.6
1983	563.3
1984	549.7
1985	600.9
1986	611.9
1987	621.8
1988	628.6
1989	623.3
1990	630.4
1991	646.5
1992	631.7
1993	613
1994	585.2
1995	507.2
1996	462.8
1997	463.1
1998	473.7
1999	455.4
2000	443.8
2001	440.5
2002	446.4
2003	427.1
2004	431.8
2005	420.1
2006	434
2007	445.9
2008	457.4
2009	462.2
2010	468.4
2011	476.6
2012	484.1
2013	493.9
2014	506.9
2015	522.2
2016	537.9
2017	554
2018	570.8