United States. Bureau of Labor Statistics. "Footnotes," in United States. Bureau of Labor Statistics. "Private Business, Nonfarm Business, and Manufacturing Sectors : Second Quarter 1977," Productivity and Costs (July 29, 1977) : 15-15. https://fraser.stlouisfed.org/title/131/item/55978/toc/494886 , accessed on April 30, 2024.