United States. Bureau of Labor Statistics. "Technical Notes," in United States. Bureau of Labor Statistics. "Second Quarter 1990 [Revised] : Business, Nonfarm Business, Manufacturing, and Nonfinancial Corporations," Productivity and Costs (September 4, 1990) : 6-6. https://fraser.stlouisfed.org/title/131/item/55914/toc/460840 , accessed on April 24, 2024.