United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "April 1983," PPI Detailed Report (April 1983) : 17-17. https://fraser.stlouisfed.org/title/63/item/21569/toc/422028 , accessed on April 18, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "April 1983," PPI Detailed Report (April 1983) : 17-17. https://fraser.stlouisfed.org/title/63/item/21569/toc/422028 , accessed on April 18, 2024.