NPR interviewed Ball State finance professor Terry Zivney, who's now a professor of finance at Ball State University in Indiana, co-authored a journal article called "The Day the United States Defaulted on Treasury Bills about a technical default on $120 Million in 1979:
""Prof. ZIVNEY: ....They said there were technical errors, word-processing errors. But I'm sure the thousands of people that did not receive their $120 million were not, you know, mollified by hearing it was just a technical difficulty.
SIEGEL: A hundred-twenty million dollars was the amount of federal debt that was at issue. You apply the dictionary definition of default, and this was a default on the debt they held. But $120 million was a tiny sliver of the Treasury's debt.
Prof. ZIVNEY: Yes, it was. The Treasury had around $800 billion outstanding at that time, so it was a very small proportion. However, professor Richard Marcus of the University of Wisconsin, Milwaukee, and I did some research. And we concluded that the defaults of 1979 raised the interest rates that the government had to pay on their securities by about six-tenths of 1 percent.
SIEGEL: Six-tenths of 1 percent - not on $120 million, but you're saying on the 800 billion, almost a trillion dollars.
Prof. ZIVNEY: Yes. And so six-tenths of 1 percent of a trillion dollars is around $6 billion a year on a $120 million mistake."