After last Thursday's stock market plunge, six major stock exchanges will, in the words of the SEC, agree upon "a structural framework, to be refined over the next day, for strengthening circuit breakers." And the Wall Street Journal reports that they will "introduce temporary trading limits on individual stock moves."

The CEOs of NYSE Euronext, Nasdaq OMX Group Inc., Bats Global Markets Inc., Direct Edge Holdings LLC, International Securities Exchange Holdings Inc. and CBOE Holdings Inc. met with the SEC yesterday and apparently "Nearly all of the exchange officials agreed that the differing rules among the various stock markets about temporarily halting or slowing trading in individual stocks worsened the decline on Thursday." Columbia University law professor John Coffee explained, "You have to agree in advance on the point at which a short-term circuit breaker would be put in. We may want the circuit breaker to kick in on a 5 percent decline."

As the investigation into what caused the nearly 1,000-point decline continues, it appears that a trade in Chicago could have pushed things to the brink. According to the WSJ, "On any other day, this $7.5 million trade for 50,000 options contracts might have briefly hurt stock prices, though not caused much of a ripple. But coming on a day when all varieties of financial markets were deeply unsettled, the trade may have played a key role in the stock-market collapse just 20 minutes later."

Last night on The Daily Show, Jon Stewart wonder why these stock market plunges are called "perfect storms" when they seem to happen so often:

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