United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "January 1983," PPI Detailed Report (January 1983) : 23-23. https://fraser.stlouisfed.org/title/63/item/21566/toc/317258 , accessed on April 25, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "January 1983," PPI Detailed Report (January 1983) : 23-23. https://fraser.stlouisfed.org/title/63/item/21566/toc/317258 , accessed on April 25, 2024.