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-. "1991," Annual Statistical Digest (November 1992) : 4-4. https://fraser.stlouisfed.org/title/7/item/23497/toc/264467 , accessed on April 18, 2024.