United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1982," PPI Detailed Report (July 1982) : 20-20. https://fraser.stlouisfed.org/title/63/item/21560/toc/194280 , accessed on April 19, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1982," PPI Detailed Report (July 1982) : 20-20. https://fraser.stlouisfed.org/title/63/item/21560/toc/194280 , accessed on April 19, 2024.