# year    value 
 1901  21.4976 
 1902 21.57106 
 1903 21.48852 
 1904 21.40062 
 1905 21.61165 
 1906 21.61799 
 1907 21.28025 
 1908 21.54501 
 1909 21.34453 
 1910  21.4157 
 1911 21.46043 
 1912 21.54206 
 1913  21.3019 
 1914 21.69436 
 1915 21.74191 
 1916 21.49393 
 1917 21.45272 
 1918 21.47188 
 1919 21.69628 
 1920 21.43499 
 1921  21.5145 
 1922 21.65934 
 1923 21.77129 
 1924 21.85079 
 1925 21.60789 
 1926 21.84527 
 1927 21.92579 
 1928 21.64265 
 1929 21.62461 
 1930 21.77039 
 1931 21.77957 
 1932 21.77232 
 1933 21.79448 
 1934 21.58061 
 1935 21.76143 
 1936 21.46885 
 1937 21.72816 
 1938 21.51876 
 1939 22.00351 
 1940 21.73529 
 1941 22.15098 
 1942 21.92366 
 1943 21.76409 
 1944 22.08282 
 1945 22.08849 
 1946 21.87663 
 1947 21.84377 
 1948 21.96065 
 1949  21.5462 
 1950 21.64349 
 1951 21.69867 
 1952 21.70792 
 1953 22.05121 
 1954 21.42795 
 1955 21.76143 
 1956 21.31255 
 1957  21.4162 
 1958 21.75006 
 1959 21.68563 
 1960 21.76666 
 1961 21.88943 
 1962 21.71881 
 1963 21.70967 
 1964    21.45 
 1965 21.46105 
 1966  21.8108 
 1967 21.63526 
 1968 21.46143 
 1969 21.40378 
 1970 21.56742 
 1971 21.43232 
 1972 21.60384 
 1973 21.66511 
 1974 21.50507 
 1975 21.73128 
 1976 21.08666 
 1977 21.71677 
 1978 21.75493 
 1979 21.73264 
 1980 21.67002 
 1981 21.92825 
 1982 21.57737 
 1983 21.78814 
 1984 21.72144 
 1985 21.64987 
 1986  21.6269 
 1987 21.74323 
 1988  21.9882 
 1989 21.52962 
 1990 21.81025 
 1991 21.93002 
 1992 21.39292 
 1993  21.3744 
 1994 21.98528 
 1995 22.05748 
 1996  21.5928 
 1997 21.97749 
 1998 22.25355 
 1999 22.03003 
 2000 22.13461 
 2001 22.08937 
 2002 22.30508 
 2003 21.89369 
 2004  21.8891 
 2005 22.41537 
 2006  22.3949 
 2007 22.36213 
 2008 22.13195 
 2009 22.30497 
 2010 22.52256 
 2011 22.36014 
 2012 22.39307 
 2013 22.35795 
 2014 22.24924 
 2015 22.18653 
 2016 22.62453 
 2017 22.50738 
 2018 22.65259