United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1983," PPI Detailed Report (July 1983) : 18-18. https://fraser.stlouisfed.org/title/63/item/21572/toc/192869 , accessed on April 23, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1983," PPI Detailed Report (July 1983) : 18-18. https://fraser.stlouisfed.org/title/63/item/21572/toc/192869 , accessed on April 23, 2024.