Board of Governors of the Federal Reserve System (U.S.), 1935-. "Summary Groupings, Seasonally Adjusted," in Board of Governors of the Federal Reserve System (U.S.), 1935-. "April 15, 1981," G.12.3 Industrial Production (1981-04-15) : 14-14. https://fraser.stlouisfed.org/title/55/item/59643/toc/472179 , accessed on April 18, 2024.