United States. Bureau of the Census. "Comparisons from Specific Peak and Trough Levels and Specific Trough Dates," in United States. Bureau of the Census. "April 1965," Business Conditions Digest (April 1965) : 70-70. https://fraser.stlouisfed.org/title/43/item/7214/toc/135675 , accessed on March 29, 2024.