United States. Department of the Treasury. "Bill offering on monthly bills, April 17, 1968, Release Number f-1220," in United States. Department of the Treasury. "Volume 161," Press Releases of the United States Department of the Treasury (March 4, 1968 - June 3, 1968) : 185-187. https://fraser.stlouisfed.org/title/6111/item/587004/toc/541024 , accessed on June 24, 2024.