# year value 1901 22.08272 1902 22.25191 1903 22.23969 1904 21.5494 1905 21.70416 1906 21.98083 1907 21.9215 1908 22.11218 1909 21.94812 1910 21.70429 1911 21.85509 1912 22.63095 1913 22.36211 1914 22.41043 1915 22.36491 1916 22.19943 1917 21.93787 1918 21.75458 1919 22.60209 1920 22.40419 1921 21.90127 1922 22.20999 1923 22.04965 1924 22.20693 1925 22.12915 1926 22.72794 1927 22.33992 1928 22.12202 1929 22.32247 1930 22.43662 1931 22.51603 1932 22.37646 1933 22.09635 1934 21.90829 1935 22.18823 1936 22.31527 1937 22.40198 1938 22.3292 1939 22.46891 1940 22.00142 1941 22.26259 1942 22.6486 1943 22.65152 1944 22.31507 1945 22.71541 1946 22.39746 1947 22.30907 1948 22.1076 1949 22.25144 1950 21.89046 1951 21.55655 1952 22.20271 1953 22.16726 1954 22.05239 1955 22.21418 1956 21.44579 1957 21.84632 1958 22.45846 1959 21.86459 1960 22.35057 1961 22.37901 1962 22.16563 1963 22.29815 1964 22.58018 1965 22.27382 1966 22.21557 1967 22.10114 1968 22.37534 1969 22.56135 1970 22.54603 1971 21.76218 1972 22.44195 1973 22.7478 1974 21.41939 1975 21.58692 1976 21.84695 1977 22.16792 1978 21.95065 1979 22.15624 1980 22.33867 1981 22.00096 1982 22.06867 1983 22.79031 1984 22.22397 1985 21.84554 1986 22.19798 1987 22.61905 1988 22.43472 1989 22.56075 1990 22.37324 1991 22.24306 1992 22.24752 1993 22.08525 1994 22.1906 1995 22.58458 1996 22.31479 1997 22.05971 1998 22.73284 1999 22.3095 2000 22.0106 2001 22.38403 2002 22.19641 2003 22.53762 2004 22.44761 2005 22.69118 2006 22.30459 2007 22.57549 2008 22.02238 2009 22.31846 2010 22.69423 2011 22.15176 2012 22.40526 2013 22.55 2014 22.5975 2015 22.43178 2016 23.1951 2017 22.90455 2018 22.47798