United States. Bureau of the Census. "Leading Indicators," in United States. Bureau of the Census. "July 1968," Business Conditions Digest (July 1968) : 62-63. https://fraser.stlouisfed.org/title/43/item/7253/toc/409169 , accessed on May 5, 2024.
United States. Bureau of the Census. "Leading Indicators," in United States. Bureau of the Census. "July 1968," Business Conditions Digest (July 1968) : 62-63. https://fraser.stlouisfed.org/title/43/item/7253/toc/409169 , accessed on May 5, 2024.