United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "May 1985," PPI Detailed Report (May 1985) : 13-13. https://fraser.stlouisfed.org/title/63/item/21594/toc/131602 , accessed on April 19, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "May 1985," PPI Detailed Report (May 1985) : 13-13. https://fraser.stlouisfed.org/title/63/item/21594/toc/131602 , accessed on April 19, 2024.