# year    value 
 1901 26.29595 
 1902 26.36263 
 1903 26.37117 
 1904  25.8048 
 1905  26.1256 
 1906 26.58009 
 1907 26.05371 
 1908  26.1712 
 1909 26.16968 
 1910 26.08022 
 1911 26.01374 
 1912  26.6443 
 1913 26.10997 
 1914 26.36329 
 1915 26.45035 
 1916 26.26833 
 1917  25.7083 
 1918 25.65747 
 1919 26.29482 
 1920 26.24228 
 1921 26.02561 
 1922 26.27824 
 1923 26.23841 
 1924 26.24769 
 1925 25.87042 
 1926 26.71565 
 1927 26.18892 
 1928 26.27727 
 1929 26.34026 
 1930 26.09372 
 1931 26.43534 
 1932 26.38717 
 1933  26.2839 
 1934  25.9645 
 1935 26.19885 
 1936 26.34342 
 1937 26.30809 
 1938 26.26461 
 1939 26.38504 
 1940 26.21478 
 1941 26.44175 
 1942 26.61351 
 1943 26.15472 
 1944 26.30134 
 1945 26.43086 
 1946 26.27877 
 1947 26.56905 
 1948 26.17032 
 1949 26.20285 
 1950  26.1578 
 1951 25.83917 
 1952 26.44891 
 1953 26.13946 
 1954 26.22591 
 1955 26.15005 
 1956 25.84421 
 1957 25.99443 
 1958  26.6439 
 1959 26.33767 
 1960 26.25371 
 1961 26.24132 
 1962 26.24294 
 1963 26.18059 
 1964 26.47804 
 1965 26.17003 
 1966 26.40114 
 1967 26.16253 
 1968 26.21763 
 1969 26.53915 
 1970 26.51541 
 1971 26.20078 
 1972 25.99117 
 1973 26.91058 
 1974 25.66954 
 1975 25.82642 
 1976 25.59687 
 1977  26.3611 
 1978 26.36371 
 1979 26.20657 
 1980 26.49651 
 1981 26.28798 
 1982 26.45513 
 1983 26.92272 
 1984  26.2751 
 1985 26.44633 
 1986 26.43982 
 1987 26.55224 
 1988 26.80045 
 1989 26.21851 
 1990  26.4331 
 1991 26.61273 
 1992 26.58288 
 1993 26.29125 
 1994 26.46858 
 1995 26.66236 
 1996 26.48891 
 1997 26.41861 
 1998 27.16506 
 1999 26.57121 
 2000 26.24139 
 2001 26.46054 
 2002 26.44065 
 2003 26.95838 
 2004 26.82627 
 2005 26.98779 
 2006 26.78477 
 2007 26.76788 
 2008 26.42932 
 2009 26.59652 
 2010 26.99369 
 2011 26.42605 
 2012 26.42794 
 2013 26.93982 
 2014 26.70016 
 2015 26.83075 
 2016  27.2827 
 2017 26.90641 
 2018 26.80783