# year    value 
 1901 -30.30362 
 1902 -29.07364 
 1903 -29.68413 
 1904 -30.15737 
 1905 -27.95452 
 1906 -30.63188 
 1907 -29.69548 
 1908 -29.77121 
 1909 -30.7691 
 1910 -29.74295 
 1911 -30.2251 
 1912 -28.70828 
 1913 -30.6662 
 1914 -28.09108 
 1915 -29.61339 
 1916 -30.21543 
 1917 -30.61287 
 1918 -29.88185 
 1919 -31.15431 
 1920 -28.60157 
 1921 -29.08816 
 1922 -30.03772 
 1923 -28.90442 
 1924 -29.71678 
 1925 -29.34468 
 1926 -27.67142 
 1927 -29.23881 
 1928 -28.42398 
 1929 -28.13593 
 1930 -29.49821 
 1931 -29.55859 
 1932 -29.12344 
 1933 -30.38989 
 1934 -27.98419 
 1935 -27.93086 
 1936 -29.66859 
 1937 -27.9661 
 1938 -27.89751 
 1939 -29.00903 
 1940 -26.85889 
 1941 -29.00514 
 1942 -28.03923 
 1943 -28.01947 
 1944 -27.11481 
 1945 -27.37854 
 1946 -29.5192 
 1947 -29.91336 
 1948 -28.20255 
 1949 -29.6902 
 1950 -29.05042 
 1951 -30.57473 
 1952 -29.65643 
 1953 -28.91625 
 1954 -29.48035 
 1955 -29.05871 
 1956 -29.55332 
 1957 -28.79287 
 1958 -29.47303 
 1959 -28.64233 
 1960 -28.79745 
 1961 -27.58362 
 1962 -28.08043 
 1963 -26.60065 
 1964 -28.13139 
 1965 -30.86512 
 1966 -32.3012 
 1967 -29.46476 
 1968 -27.98418 
 1969 -31.51501 
 1970 -28.13146 
 1971 -30.03747 
 1972 -30.41623 
 1973 -29.07682 
 1974 -29.99425 
 1975 -29.53876 
 1976 -29.2139 
 1977 -27.89181 
 1978 -28.2867 
 1979 -30.46081 
 1980 -27.82147 
 1981 -26.43063 
 1982 -29.06185 
 1983 -28.07031 
 1984 -28.21398 
 1985 -28.49356 
 1986 -26.31694 
 1987 -28.21693 
 1988 -28.28537 
 1989 -27.23291 
 1990 -29.36905 
 1991 -28.48977 
 1992 -27.49366 
 1993 -27.27651 
 1994 -29.05486 
 1995 -27.2025 
 1996 -27.66668 
 1997 -27.81101 
 1998 -28.30791 
 1999 -28.97527 
 2000 -27.57427 
 2001 -27.71272 
 2002 -28.24946 
 2003 -26.77511 
 2004 -27.58515 
 2005 -28.2019 
 2006 -27.62867 
 2007 -26.75649 
 2008 -27.41064 
 2009 -28.82544 
 2010 -27.60435 
 2011 -27.82551 
 2012 -27.27743 
 2013  -28.596 
 2014 -26.26228 
 2015 -25.55787 
 2016 -25.20188 
 2017 -26.34813 
 2018 -25.72785