United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "February 1986," PPI Detailed Report (February 1986) : 15-17. https://fraser.stlouisfed.org/title/63/item/21603/toc/260088 , accessed on April 19, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "February 1986," PPI Detailed Report (February 1986) : 15-17. https://fraser.stlouisfed.org/title/63/item/21603/toc/260088 , accessed on April 19, 2024.