# year    value 
 1901 26.65418 
 1902 26.82618 
 1903 26.47895 
 1904  26.4484 
 1905 26.33264 
 1906 26.64971 
 1907 26.25173 
 1908 26.70712 
 1909  26.7089 
 1910 26.33553 
 1911 26.29203 
 1912 26.60961 
 1913 26.23648 
 1914 26.53224 
 1915 26.54365 
 1916 26.59562 
 1917 26.16128 
 1918 26.17745 
 1919 26.65244 
 1920 26.40115 
 1921 26.64404 
 1922 26.59297 
 1923 26.49538 
 1924  26.9649 
 1925 26.70988 
 1926 26.51982 
 1927  26.5139 
 1928 26.83156 
 1929 26.68213 
 1930 26.51953 
 1931 26.86891 
 1932  26.6499 
 1933 26.66135 
 1934 26.68451 
 1935  26.8907 
 1936 26.99416 
 1937 26.86878 
 1938  26.8744 
 1939 26.72905 
 1940 26.69888 
 1941 27.15628 
 1942 26.98748 
 1943 26.35607 
 1944 26.64737 
 1945 26.48214 
 1946  26.7277 
 1947 26.86167 
 1948 26.58036 
 1949  26.6601 
 1950 26.38404 
 1951 26.63647 
 1952 26.77321 
 1953 26.73451 
 1954 26.72708 
 1955 26.66236 
 1956 26.52728 
 1957 26.24817 
 1958 27.26496 
 1959 26.81934 
 1960 26.55221 
 1961 26.69648 
 1962 26.64534 
 1963 26.39919 
 1964 26.91835 
 1965 26.29733 
 1966 26.66183 
 1967 26.33303 
 1968 26.16718 
 1969 27.22483 
 1970 26.79346 
 1971 26.49604 
 1972 26.45858 
 1973 27.04675 
 1974 26.60133 
 1975   26.658 
 1976 26.25059 
 1977 26.69713 
 1978 26.89965 
 1979 26.88065 
 1980 27.22942 
 1981 26.96493 
 1982 26.61808 
 1983 26.90327 
 1984 27.14163 
 1985 26.91809 
 1986 26.91447 
 1987 26.99568 
 1988 27.36547 
 1989 26.68883 
 1990 26.95233 
 1991 27.05576 
 1992 26.73382 
 1993 26.83613 
 1994 27.09891 
 1995 27.00806 
 1996  27.0491 
 1997 26.74529 
 1998 27.60032 
 1999 27.24165 
 2000 27.26149 
 2001 27.53921 
 2002 27.60995 
 2003 27.52179 
 2004 27.51298 
 2005 27.59859 
 2006  27.3511 
 2007 27.56115 
 2008 27.46767 
 2009 27.49577 
 2010 28.13075 
 2011 27.42112 
 2012 27.37896 
 2013 27.60174 
 2014 27.48058 
 2015 27.46672 
 2016 27.98339 
 2017 27.59388 
 2018 27.57356