# year    value 
 1901 16.47917 
 1902 16.47746 
 1903 16.25743 
 1904 16.36846 
 1905 16.90783 
 1906 16.41666 
 1907 16.31391 
 1908 16.26161 
 1909 16.78509 
 1910 15.96483 
 1911  16.1656 
 1912 15.94148 
 1913 16.55719 
 1914 16.52126 
 1915 17.09618 
 1916 16.03407 
 1917 16.05288 
 1918 16.38776 
 1919 16.28155 
 1920 16.78282 
 1921  16.2351 
 1922 16.54835 
 1923 16.39755 
 1924 16.35234 
 1925 17.04157 
 1926 16.23994 
 1927 16.84402 
 1928 16.46505 
 1929 16.41241 
 1930 16.40607 
 1931 16.52223 
 1932 16.58638 
 1933 16.42865 
 1934 15.79635 
 1935 16.50941 
 1936  17.1527 
 1937 16.37182 
 1938   16.616 
 1939 16.61341 
 1940  17.0574 
 1941  17.1032 
 1942 17.01702 
 1943 16.49692 
 1944 16.33371 
 1945 17.01574 
 1946 16.92312 
 1947 16.62103 
 1948  16.3191 
 1949 16.07883 
 1950  15.7281 
 1951 17.08055 
 1952 16.02357 
 1953 16.46299 
 1954 16.47058 
 1955 16.53316 
 1956 16.27774 
 1957 16.52726 
 1958 16.27989 
 1959 16.48804 
 1960 16.34168 
 1961  16.3922 
 1962 16.00167 
 1963 17.04811 
 1964 16.34691 
 1965 17.10299 
 1966   16.449 
 1967 16.13856 
 1968 16.49286 
 1969  16.6628 
 1970 16.34044 
 1971  16.7262 
 1972 16.57067 
 1973 16.61015 
 1974 16.62469 
 1975 16.61302 
 1976 16.09927 
 1977 17.35674 
 1978 17.00733 
 1979 17.00422 
 1980 17.43102 
 1981 16.10292 
 1982 16.90837 
 1983 17.13499 
 1984   16.533 
 1985 16.38808 
 1986  16.5564 
 1987 16.78516 
 1988  17.3487 
 1989 17.00763 
 1990 17.52651 
 1991  16.9601 
 1992 16.37935 
 1993 16.44514 
 1994 17.10175 
 1995 17.45631 
 1996 16.68775 
 1997 16.72734 
 1998 17.94149 
 1999 17.56322 
 2000 16.64663 
 2001 17.68698 
 2002 17.29709 
 2003 17.27917 
 2004 17.45448 
 2005 17.80905 
 2006 18.20916 
 2007 17.50042 
 2008 17.77808 
 2009 17.26762 
 2010 17.89367 
 2011 17.48005 
 2012 16.85178 
 2013 17.67874 
 2014 17.53065 
 2015 17.54436 
 2016 17.19719 
 2017 17.73905 
 2018  17.1247