# year    value 
 1900 17.06494 
 1901 16.90869 
 1902 16.99318 
 1903 16.58911 
 1904 16.80498 
 1905 16.84756 
 1906 16.95083 
 1907 16.77403 
 1908 16.84276 
 1909 16.95815 
 1910 17.11731 
 1911 16.99724 
 1912 16.75907 
 1913 16.63787 
 1914 16.93119 
 1915 17.09744 
 1916 17.03426 
 1917 17.12633 
 1918 17.21979 
 1919 17.00491 
 1920 17.15426 
 1921 17.05875 
 1922  17.0218 
 1923 17.14966 
 1924 17.27492 
 1925 17.18515 
 1926  17.1627 
 1927 17.19534 
 1928 17.30694 
 1929  17.1638 
 1930 17.16161 
 1931 17.10331 
 1932  17.1877 
 1933 17.17856 
 1934 17.13597 
 1935 17.16371 
 1936 17.33861 
 1937 17.21238 
 1938 17.34554 
 1939 17.19535 
 1940  17.3438 
 1941 17.32712 
 1942 17.22266 
 1943 17.39795 
 1944 17.31305 
 1945 17.34256 
 1946 17.22115 
 1947 17.28405 
 1948 17.40978 
 1949 17.25831 
 1950 17.37782 
 1951 17.32464 
 1952 17.19236 
 1953 16.97064 
 1954 17.24786 
 1955 17.11196 
 1956  17.2446 
 1957 17.19389 
 1958 17.26799 
 1959 17.24613 
 1960 17.23908 
 1961  17.2184 
 1962 17.15058 
 1963 17.19744 
 1964 16.98136 
 1965 17.07056 
 1966 17.10143 
 1967 17.18065 
 1968  17.1672 
 1969 17.14111 
 1970 17.37538 
 1971 17.37391 
 1972 17.25592 
 1973 17.30598 
 1974 17.26471 
 1975 17.39938 
 1976 17.34184 
 1977  17.2818 
 1978 17.36147 
 1979 17.47654 
 1980 17.62629 
 1981 17.53003 
 1982 17.42117 
 1983 17.04072 
 1984 17.22214 
 1985 17.39934 
 1986 17.43253 
 1987 17.55036 
 1988 17.56855 
 1989 17.70027 
 1990 17.75623 
 1991 17.68582 
 1992 17.30779 
 1993 17.57039 
 1994 17.58204 
 1995 17.57772 
 1996 17.78357 
 1997 18.00176 
 1998 17.90386 
 1999 17.95108 
 2000 18.10461 
 2001 18.20576 
 2002 18.05721 
 2003 18.05083 
 2004 18.06428 
 2005 18.30079