# year    value 
 1901 16.34165 
 1902 16.07206 
 1903 16.07331 
 1904 16.09345 
 1905 16.22297 
 1906 16.23978 
 1907 15.86414 
 1908 16.26121 
 1909 16.15672 
 1910 16.22158 
 1911 16.08014 
 1912 15.87811 
 1913 15.96726 
 1914 16.28327 
 1915 16.26769 
 1916 16.03961 
 1917 16.15537 
 1918 16.07046 
 1919 16.16931 
 1920 16.09947 
 1921  16.2573 
 1922 16.31182 
 1923 16.25012 
 1924 16.33363 
 1925 16.24594 
 1926 16.46904 
 1927 16.39173 
 1928  16.3377 
 1929 16.17142 
 1930 16.40657 
 1931 16.42439 
 1932 16.30276 
 1933 16.30589 
 1934 16.34679 
 1935 16.35424 
 1936  16.3817 
 1937 16.41187 
 1938 16.36414 
 1939 16.55177 
 1940 16.47079 
 1941 16.64677 
 1942 16.37858 
 1943 16.30236 
 1944 16.55408 
 1945 16.48081 
 1946 16.47334 
 1947 16.34728 
 1948 16.48192 
 1949 16.23867 
 1950 16.33176 
 1951 16.33164 
 1952 16.42418 
 1953  16.5396 
 1954  16.2526 
 1955 16.24438 
 1956 16.04946 
 1957 16.23513 
 1958 16.46544 
 1959 16.42751 
 1960 16.39124 
 1961 16.45256 
 1962 16.29149 
 1963 16.30469 
 1964 16.08566 
 1965 16.09486 
 1966 16.35338 
 1967 16.23065 
 1968 16.11296 
 1969  16.3532 
 1970 16.40797 
 1971 16.24578 
 1972 16.18991 
 1973 16.37697 
 1974 16.23296 
 1975 16.29736 
 1976  15.9184 
 1977 16.48486 
 1978 16.31507 
 1979 16.41696 
 1980  16.5449 
 1981 16.43357 
 1982 16.37268 
 1983 16.45467 
 1984 16.25639 
 1985 16.34756 
 1986 16.50377 
 1987 16.49796 
 1988 16.62623 
 1989  16.5118 
 1990 16.74012 
 1991 16.73964 
 1992 16.27983 
 1993   16.384 
 1994 16.91846 
 1995 16.76403 
 1996  16.5238 
 1997 16.85392 
 1998 17.20899 
 1999 16.73542 
 2000 16.88248 
 2001  17.0329 
 2002 17.08803 
 2003 16.99734 
 2004 16.82513 
 2005  17.1039 
 2006 17.19647 
 2007 17.07829 
 2008 17.00303 
 2009 17.03019 
 2010 17.17841 
 2011 17.14697 
 2012 17.18949 
 2013 17.18074 
 2014 17.19028 
 2015 17.41245 
 2016 17.43664 
 2017 17.42516 
 2018 17.32554