United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1988," PPI Detailed Report (July 1988) : 14-16. https://fraser.stlouisfed.org/title/63/item/21632/toc/109860 , accessed on March 29, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "July 1988," PPI Detailed Report (July 1988) : 14-16. https://fraser.stlouisfed.org/title/63/item/21632/toc/109860 , accessed on March 29, 2024.