# year    value 
 1940 24.53878 
 1941 24.79809 
 1942 24.59113 
 1943 24.27175 
 1944 24.40384 
 1945  24.3156 
 1946 24.47665 
 1947 24.60307 
 1948 24.31731 
 1949 24.27574 
 1950 24.09885 
 1951 24.40376 
 1952 24.43135 
 1953  24.4425 
 1954 24.29599 
 1955 24.30942 
 1956 24.12382 
 1957 24.28105 
 1958 24.63481 
 1959 24.33273 
 1960  24.4725 
 1961 24.17101 
 1962 24.32403 
 1963 24.46309 
 1964 24.17469 
 1965  24.2398 
 1966 24.48777 
 1967 24.04465 
 1968 24.15308 
 1969 24.67968 
 1970 24.39539 
 1971 24.04123 
 1972 24.35007 
 1973 24.53163 
 1974 24.13296 
 1975 24.14724 
 1976 24.17339 
 1977 24.41158 
 1978 24.44655 
 1979 24.67125 
 1980 24.70076 
 1981 24.51708 
 1982 24.42949 
 1983 24.57151 
 1984 24.47091 
 1985 24.51267 
 1986 24.49063 
 1987 24.93884 
 1988 24.70531 
 1989 24.39383 
 1990 24.80469 
 1991 24.65651 
 1992 24.36217 
 1993 24.64161 
 1994 24.63415 
 1995 24.76655 
 1996 24.76069 
 1997 24.77065 
 1998  25.2445 
 1999 24.85735 
 2000  24.7705 
 2001 25.00361 
 2002 25.11855 
 2003 25.13197 
 2004  25.0785 
 2005 25.15119 
 2006 25.10161 
 2007 25.04972 
 2008 24.89175 
 2009 25.32565 
 2010 25.48981 
 2011 25.02162 
 2012 25.04549 
 2013 25.06285 
 2014 25.09705 
 2015 25.23277 
 2016 25.41866 
 2017 25.22142 
 2018 25.13853