Year Current Prices 1919 3508.10 1920 4777.10 1921 2956.70 1922 3568.90 1923 4647.30 1924 4465.30 1925 4950.40 1926 5111.50 1927 4845.20 1928 4793.80 1929 5007.50 1930 3779.80 1931 2552.10 1932 1362.70 1933 1536.10 1934 1909.90 1935 2375.00 1936 3331.50 1937 3945.80 1938 3159.00 1939 3701.60