Year	Measure
1800	544.7
1820	544.7
1913	550.9
1950	553.4
1951	571.9
1952	575.6
1953	584
1954	601.9
1955	606.5
1956	613.7
1957	621
1958	622.6
1959	641.9
1960	645.2
1961	643.3
1962	634.2
1963	631.8
1964	645.9
1965	639
1966	738.9
1967	713.6
1968	726.4
1969	756.5
1970	782.6
1971	797.2
1972	803
1973	759.5
1974	791
1975	654.7
1976	662.9
1977	640.3
1978	647.9
1979	658.5
1980	609.8
1981	606.2
1982	572.2
1983	552
1984	531.2
1985	508.6
1986	507.8
1987	506.1
1988	490.9
1989	482
1990	556.5
1991	658.7
1992	636.6
1993	626.1
1994	644.9
1995	662.2
1996	658.5
1997	609.2
1998	551.4
1999	529.8
2000	519.5
2001	515.9
2002	531.5
2003	365.8
2004	375.7
2005	383
2006	401.3
2007	433.4
2008	437.7
2009	442.1
2010	450.1
2011	473.3
2012	499.8
2013	523.5
2014	537.5
2015	562.9
2016	578.7
2017	600.4
2018	631.2