Year Years
1800 30.8
1801 30.8
1802 30.8
1803 30.8
1804 30.8
1805 30.8
1806 30.8
1807 30.8
1808 30.8
1809 30.8
1810 30.8
1811 30.8
1812 30.8
1813 30.8
1814 30.8
1815 30.8
1816 30.8
1817 30.8
1818 30.8
1819 30.8
1820 30.8
1821 30.8
1822 30.8
1823 30.8
1824 30.8
1825 30.8
1826 30.8
1827 30.8
1828 30.8
1829 30.8
1830 30.8
1831 30.8
1832 30.8
1833 30.8
1834 30.8
1835 30.8
1836 30.8
1837 30.8
1838 30.8
1839 30.8
1840 30.8
1841 30.8
1842 30.8
1843 30.8
1844 30.8
1845 30.8
1846 30.8
1847 30.8
1848 30.8
1849 30.8
1850 30.8
1851 30.8
1852 30.8
1853 30.8
1854 30.8
1855 30.8
1856 30.8
1857 30.8
1858 30.8
1859 30.8
1860 30.8
1861 30.8
1862 30.8
1863 30.8
1864 30.8
1865 30.8
1866 30.8
1867 30.8
1868 30.8
1869 30.8
1870 30.8
1871 30.8
1872 30.79
1873 30.79
1874 30.78
1875 30.78
1876 30.77
1877 30.77
1878 30.77
1879 30.76
1880 30.76
1881 30.75
1882 30.75
1883 30.74
1884 30.74
1885 30.74
1886 30.73
1887 30.73
1888 30.72
1889 30.72
1890 30.71
1891 30.71
1892 30.7
1893 30.7
1894 30.7
1895 30.69
1896 30.69
1897 30.68
1898 30.68
1899 30.67
1900 30.67
1901 30.67
1902 30.66
1903 30.66
1904 30.65
1905 30.65
1906 30.64
1907 30.64
1908 30.64
1909 30.63
1910 30.63
1911 30.62
1912 30.62
1913 30.61
1914 30.61
1915 30.61
1916 30.6
1917 30.6
1918 25.36
1919 30.59
1920 30.58
1921 30.58
1922 30.57
1923 30.57
1924 30.57
1925 30.56
1926 30.56
1927 30.55
1928 30.55
1929 30.54
1930 30.54
1931 30.54
1932 30.53
1933 30.53
1934 30.52
1935 30.52
1936 30.51
1937 30.51
1938 30.51
1939 30.5
1940 30.5
1941 32.75
1942 35
1943 37.25
1944 39.5
1945 41.76
1946 44
1947 46.25
1948 48.5
1949 50.76
1950 53.01
1951 53.41
1952 54.21
1953 55.01
1954 55.79
1955 56.58
1956 57.34
1957 58.1
1958 58.85
1959 59.6
1960 60.34
1961 61.08
1962 61.82
1963 62.56
1964 63.29
1965 64.02
1966 64.73
1967 65.44
1968 66.12
1969 66.77
1970 67.38
1971 67.42
1972 67.47
1973 67.53
1974 68.13
1975 68.7
1976 69.38
1977 69.92
1978 70.35
1979 70.69
1980 70.8
1981 70.92
1982 70.74
1983 71.49
1984 72.8
1985 73.1
1986 73.54
1987 73.99
1988 74.23
1989 74.73
1990 75.04
1991 74.93
1992 74.98
1993 74.88
1994 74.8
1995 74.79
1996 74.9
1997 74.99
1998 75.06
1999 75.1
2000 75.31
2001 75.59
2002 75.7
2003 75.95
2004 76.41
2005 76.88
2006 77.36
2007 77.88
2008 78.37
2009 78.9
2010 79.52
2011 79.97
2012 80.22
2013 80.49
2014 80.49
2015 80.46
2016 80.41
2017 80.56
2018 80.71