Year Total 1800 6.51 1801 6.51 1802 6.51 1803 6.51 1804 6.51 1805 6.51 1806 6.51 1807 6.51 1808 6.51 1809 6.51 1810 6.51 1811 6.51 1812 6.51 1813 6.51 1814 6.51 1815 6.51 1816 6.51 1817 6.51 1818 6.51 1819 6.51 1820 6.51 1821 6.51 1822 6.51 1823 6.51 1824 6.51 1825 6.51 1826 6.51 1827 6.51 1828 6.51 1829 6.51 1830 6.51 1831 6.51 1832 6.51 1833 6.51 1834 6.51 1835 6.51 1836 6.51 1837 6.51 1838 6.51 1839 6.51 1840 6.51 1841 6.51 1842 6.51 1843 6.51 1844 6.51 1845 6.51 1846 6.51 1847 6.51 1848 6.51 1849 6.51 1850 6.51 1851 6.51 1852 6.51 1853 6.51 1854 6.51 1855 6.51 1856 6.51 1857 6.51 1858 6.51 1859 6.51 1860 6.51 1861 6.51 1862 6.51 1863 6.51 1864 6.51 1865 6.51 1866 6.51 1867 6.51 1868 6.51 1869 6.51 1870 6.51 1871 6.51 1872 6.51 1873 6.51 1874 6.51 1875 6.51 1876 6.51 1877 6.51 1878 6.51 1879 6.51 1880 6.51 1881 6.51 1882 6.51 1883 6.51 1884 6.51 1885 6.51 1886 6.51 1887 6.51 1888 6.51 1889 6.51 1890 6.51 1891 6.51 1892 6.51 1893 6.51 1894 6.51 1895 6.51 1896 6.51 1897 6.51 1898 6.51 1899 6.51 1900 6.51 1901 6.51 1902 6.51 1903 6.51 1904 6.51 1905 6.51 1906 6.51 1907 6.51 1908 6.51 1909 6.51 1910 6.51 1911 6.51 1912 6.51 1913 6.51 1914 6.51 1915 6.51 1916 6.51 1917 6.51 1918 6.51 1919 6.51 1920 6.51 1921 6.51 1922 6.51 1923 6.51 1924 6.51 1925 6.51 1926 6.54 1927 6.57 1928 6.6 1929 6.64 1930 6.67 1931 6.7 1932 6.74 1933 6.77 1934 6.8 1935 6.83 1936 6.87 1937 6.9 1938 6.93 1939 6.97 1940 7 1941 7.03 1942 7.06 1943 7.1 1944 7.13 1945 7.16 1946 7.2 1947 7.23 1948 7.26 1949 7.29 1950 7.33 1951 7.32 1952 7.3 1953 7.29 1954 7.29 1955 7.29 1956 7.31 1957 7.33 1958 7.35 1959 7.36 1960 7.36 1961 7.35 1962 7.3 1963 7.23 1964 7.12 1965 6.97 1966 6.8 1967 6.59 1968 6.37 1969 6.15 1970 5.94 1971 5.76 1972 5.62 1973 5.51 1974 5.45 1975 5.43 1976 5.44 1977 5.47 1978 5.51 1979 5.54 1980 5.55 1981 5.53 1982 5.48 1983 5.39 1984 5.27 1985 5.13 1986 4.99 1987 4.86 1988 4.76 1989 4.69 1990 4.64 1991 4.61 1992 4.58 1993 4.55 1994 4.5 1995 4.45 1996 4.39 1997 4.34 1998 4.3 1999 4.27 2000 4.25 2001 4.24 2002 4.22 2003 4.2 2004 4.18 2005 4.14 2006 4.1 2007 4.06 2008 4.01 2009 3.96 2010 3.91 2011 3.86 2012 3.82 2013 3.77 2014 3.72 2015 3.68 2016 3.64 2017 3.6 2018 3.56