# year    value 
 1901 23.37117 
 1902 23.27242 
 1903 23.06195 
 1904 23.04787 
 1905 23.05975 
 1906 23.21901 
 1907 22.94486 
 1908 23.08637 
 1909 23.01082 
 1910  22.9927 
 1911 22.94067 
 1912 23.28299 
 1913 23.36404 
 1914 23.21547 
 1915 23.22571 
 1916 22.97917 
 1917 22.87783 
 1918 23.05056 
 1919 23.34309 
 1920 23.14849 
 1921 22.82915 
 1922 22.90141 
 1923 22.92936 
 1924 22.95269 
 1925 23.14952 
 1926 23.42266 
 1927 23.10233 
 1928 22.95677 
 1929 23.16028 
 1930 23.17725 
 1931 22.97416 
 1932 23.23635 
 1933 23.03065 
 1934  22.8862 
 1935 23.20155 
 1936 23.22637 
 1937 23.32303 
 1938 23.11747 
 1939  23.2257 
 1940 23.33772 
 1941 23.35032 
 1942 23.18256 
 1943 23.35796 
 1944 23.59343 
 1945 23.57566 
 1946 23.18969 
 1947  23.1428 
 1948  23.1592 
 1949 22.96074 
 1950 22.91289 
 1951 23.05817 
 1952 22.94116 
 1953 23.18388 
 1954 22.90844 
 1955 22.77023 
 1956 22.42496 
 1957 22.93787 
 1958 23.23839 
 1959 22.96468 
 1960 23.04114 
 1961 23.53576 
 1962 23.28892 
 1963 23.49799 
 1964 23.14413 
 1965 23.43518 
 1966  23.3583 
 1967 23.38035 
 1968 23.30039 
 1969 23.77003 
 1970 23.50528 
 1971 23.00112 
 1972 23.37835 
 1973 23.01534 
 1974 22.68751 
 1975 22.88821 
 1976 22.73057 
 1977 23.14949 
 1978 23.06869 
 1979 23.05942 
 1980 23.25384 
 1981 23.01232 
 1982 23.23215 
 1983 23.30969 
 1984 22.90222 
 1985 23.19921 
 1986 23.24269 
 1987 23.52639 
 1988 23.24073 
 1989 23.17983 
 1990 23.17144 
 1991 23.33536 
 1992 23.22632 
 1993 23.21461 
 1994  23.5912 
 1995 23.46278 
 1996 23.17861 
 1997 23.66198 
 1998 23.59657 
 1999  22.9842 
 2000 23.08875 
 2001 23.30739 
 2002 23.40793 
 2003 23.42965 
 2004 23.49982 
 2005 23.37554 
 2006 23.53077 
 2007 23.04544 
 2008  23.2978 
 2009 23.58581 
 2010  23.4805 
 2011 23.42507 
 2012 23.61374 
 2013 23.47103 
 2014 23.70729 
 2015 23.99973 
 2016 23.62736 
 2017 23.74026 
 2018 23.44445