United States. Bureau of Labor Statistics. "Durable Manufacturing Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "First Quarter 1991 [Preliminary]," Productivity and Costs (May 8, 1991) : 17-17. https://fraser.stlouisfed.org/title/131/item/55754/toc/463046 , accessed on May 4, 2024.