United States. Bureau of the Census. "Leading Indicators," in United States. Bureau of the Census. "May 1968," Business Conditions Digest (May 1968) : 59-59. https://fraser.stlouisfed.org/title/43/item/7251/toc/131250 , accessed on April 19, 2024.
United States. Bureau of the Census. "Leading Indicators," in United States. Bureau of the Census. "May 1968," Business Conditions Digest (May 1968) : 59-59. https://fraser.stlouisfed.org/title/43/item/7251/toc/131250 , accessed on April 19, 2024.