United States. Bureau of Labor Statistics. "Manufacturing Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "First Quarter 1991 [Preliminary]," Productivity and Costs (May 8, 1991) : 16-16. https://fraser.stlouisfed.org/title/131/item/55754/toc/463045 , accessed on May 7, 2024.