Board of Governors of the Federal Reserve System (U.S.), 1935-. "Symbols and Abbreviations," in Board of Governors of the Federal Reserve System (U.S.), 1935-. "1973-1977," Annual Statistical Digest (December 1978) : 4-4. https://fraser.stlouisfed.org/title/7/item/23504/toc/110102 , accessed on April 21, 2024.