Board of Governors of the Federal Reserve System (U.S.), 1935- and Federal Reserve Board, 1914-1935. "Industrial Production - Indexes and Gross Value," in Board of Governors of the Federal Reserve System (U.S.), 1935- and Federal Reserve Board, 1914-1935. "April 1991," Federal Reserve Bulletin (April 1991) : 134-135. https://fraser.stlouisfed.org/title/62/item/20827/toc/113363 , accessed on April 23, 2024.