United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "March 1984," PPI Detailed Report (March 1984) : 13-13. https://fraser.stlouisfed.org/title/63/item/21580/toc/207518 , accessed on April 19, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "March 1984," PPI Detailed Report (March 1984) : 13-13. https://fraser.stlouisfed.org/title/63/item/21580/toc/207518 , accessed on April 19, 2024.