# year    value 
 1901 23.37522 
 1902  23.4601 
 1903 23.26167 
 1904 23.14972 
 1905  23.3763 
 1906 23.32659 
 1907 23.15536 
 1908 23.28138 
 1909 23.18083 
 1910 23.26166 
 1911 23.22972 
 1912 23.14604 
 1913 23.00872 
 1914 23.17474 
 1915 23.43975 
 1916 23.20261 
 1917 23.19268 
 1918 23.12466 
 1919 23.22447 
 1920 23.17112 
 1921 23.30148 
 1922  23.2811 
 1923 23.25765 
 1924 23.39885 
 1925 23.38167 
 1926 23.50138 
 1927  23.3962 
 1928 23.43848 
 1929 23.22026 
 1930 23.28803 
 1931 23.44589 
 1932 23.45199 
 1933 23.34236 
 1934 23.39588 
 1935 23.29122 
 1936 23.28318 
 1937 23.40304 
 1938 23.22407 
 1939 23.33944 
 1940 23.48003 
 1941 23.58124 
 1942 23.37446 
 1943 23.23919 
 1944 23.44763 
 1945 23.54617 
 1946 23.46027 
 1947 23.57346 
 1948 23.39778 
 1949 23.25306 
 1950 23.05989 
 1951 23.45502 
 1952 23.34354 
 1953 23.61977 
 1954 23.13049 
 1955 23.05254 
 1956 23.00106 
 1957  23.3786 
 1958 23.47185 
 1959   23.343 
 1960 23.43177 
 1961  23.2703 
 1962 23.25009 
 1963 23.38831 
 1964 23.11687 
 1965 23.13058 
 1966 23.31576 
 1967 23.20058 
 1968  23.0311 
 1969 23.42771 
 1970  23.3207 
 1971 22.96237 
 1972 23.41532 
 1973 23.32274 
 1974 23.03859 
 1975 23.10898 
 1976 23.03597 
 1977 23.44657 
 1978 23.38152 
 1979 23.55542 
 1980 23.61654 
 1981 23.49079 
 1982 23.55801 
 1983 23.86693 
 1984 23.30384 
 1985  23.2854 
 1986 23.44248 
 1987 23.77571 
 1988 23.56896 
 1989   23.477 
 1990 23.66239 
 1991 23.54321 
 1992 23.51337 
 1993 23.65424 
 1994 23.64395 
 1995 23.75783 
 1996  23.5496 
 1997 23.79733 
 1998 24.15497 
 1999 23.51828 
 2000 23.64115 
 2001 23.71974 
 2002 23.92301 
 2003 23.87795 
 2004 23.68953 
 2005 23.97143 
 2006 23.98159 
 2007 23.76103 
 2008 23.63052 
 2009  24.2707 
 2010 24.00468 
 2011 24.12034 
 2012 23.94353 
 2013 23.97814 
 2014 24.13387 
 2015 24.18944 
 2016   24.226 
 2017 24.14643 
 2018 24.10462