# year    value 
 1901  16.2813 
 1902 16.59471 
 1903 15.96579 
 1904 16.16251 
 1905 15.97771 
 1906 16.19457 
 1907 16.02659 
 1908 16.10495 
 1909   16.262 
 1910 15.95334 
 1911 16.04165 
 1912 16.24581 
 1913 16.12689 
 1914 16.53658 
 1915 16.65557 
 1916 16.10717 
 1917 15.99942 
 1918 15.98647 
 1919   16.123 
 1920 16.06543 
 1921  16.3473 
 1922  16.4769 
 1923 16.31497 
 1924 16.39868 
 1925 16.36691 
 1926 16.38982 
 1927  16.2602 
 1928 16.25455 
 1929 16.08101 
 1930  16.1062 
 1931 16.17441 
 1932 16.42745 
 1933  16.1326 
 1934 15.91365 
 1935 16.20834 
 1936 16.08026 
 1937 16.01209 
 1938 16.46407 
 1939 16.56912 
 1940 16.71359 
 1941 17.14828 
 1942 16.63311 
 1943 16.31829 
 1944 16.31928 
 1945 16.15601 
 1946 16.70512 
 1947  16.4101 
 1948 16.62124 
 1949 16.19214 
 1950 15.92775 
 1951 16.28744 
 1952 16.25155 
 1953 16.70427 
 1954 15.94704 
 1955 16.44051 
 1956 16.01603 
 1957 15.90062 
 1958 16.75738 
 1959 16.36654 
 1960 16.33676 
 1961 16.54207 
 1962 16.37156 
 1963 16.78166 
 1964 16.08391 
 1965  16.6067 
 1966 16.64464 
 1967 16.13021 
 1968 16.21312 
 1969 16.02613 
 1970 16.28099 
 1971 16.33781 
 1972 16.08172 
 1973 16.67948 
 1974 16.13913 
 1975 16.45615 
 1976 16.13602 
 1977 16.62724 
 1978 16.63936 
 1979 16.80419 
 1980 16.73986 
 1981 16.64328 
 1982 16.61177 
 1983  16.6878 
 1984 16.05778 
 1985 16.45841 
 1986 16.50303 
 1987 16.91281 
 1988 16.96849 
 1989 16.69314 
 1990 16.95701 
 1991 16.71741 
 1992 16.55476 
 1993 16.49739 
 1994 16.90744 
 1995 16.95743 
 1996 16.53271 
 1997 16.92199 
 1998 17.43344 
 1999 17.41866 
 2000 17.07427 
 2001 17.30482 
 2002 17.54243 
 2003 16.99337 
 2004  17.5784 
 2005 17.11073 
 2006  17.6016 
 2007 17.67275 
 2008 17.22116 
 2009 17.53992 
 2010 17.44848 
 2011 16.98101 
 2012 16.72462 
 2013 17.39005 
 2014 17.08767 
 2015 17.56532 
 2016 17.72997 
 2017 17.69404 
 2018 17.41986