The fear index is not merely an indicator. The Chicago Exchange does a steady business trading bets on whether the VIX will go up or down. In these strange times, you can essentially buy and sell fear.

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The computer spits out a number called the volatility index, or VIX. It's a reading of how scared people are. "That's in fact what it measures," Whaley said. That reading provides insight into future wavering in the market, what traders call volatility.

The details of Whaley's formula are complicated. The VIX gets its magic number by analyzing the price of a kind of insurance policy against stock market declines. "What VIX measures, to some extent, is the amount people are willing to pay for insurance," he explained.

On Thursday, Whaley stared at numbers from a fairly nervous market. The VIX indicated people thought the stock market might go up or down by almost 9 percent over the next 30 days.

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Another measure of market anxiety is called the TED Spread. By considering the demand for Treasury bills, the euro and the dollar, it renders a number on how scared banks are that another bank might collapse.

Jeff Frankel, an economist at Harvard, said that for years the TED Spread was tiny and steady and dull. "It always used to be very boring," he said, "so I never used to keep an eye on it at all. It's not boring now."

Sometime around June 2007, he remembers, the TED Spread shot up -- and stayed high. "You know, for it to shoot up temporarily is OK," he said. "But for it to stay up! It is really quite remarkable. It's one reason why people say this is the worst financial crisis since the Great Depression, because so far as I know this has not happened before."