United States. Bureau of Labor Statistics. "Contents," in United States. Bureau of Labor Statistics. "April 1981," PPI Detailed Report (April 1981) : 3-3. https://fraser.stlouisfed.org/title/63/item/21545/toc/417581 , accessed on April 23, 2024.
United States. Bureau of Labor Statistics. "Contents," in United States. Bureau of Labor Statistics. "April 1981," PPI Detailed Report (April 1981) : 3-3. https://fraser.stlouisfed.org/title/63/item/21545/toc/417581 , accessed on April 23, 2024.