Source: D. T. Max. “Jim Simons, the Numbers King.” The New Yorker, December 18 & 25, 2017 Issue
He hired another mathematician, whom he’d met at the I.D.A., and they began to create models that predicted the direction of currency prices. Simons told me that he staffed his “crazy hedge fund”—the company that became Renaissance Technologies—not with financiers but with physicists, astronomers, and mathematicians. He also invested heavily in computers and in the people who ran them. “If you’re going to analyze data, it really has to be clean,” he said. “Suppose it’s a series of stock prices. 31¼, 62½. Wait, stocks don’t double in a day—so there’s an error in the data! There’s all kinds of ways to get bugs out of data, and it’s important, because they can really screw you up.”
Please explain the bolded?