Note how the advances minus declines for the NYSE deteriorated (bottom chart) prior to the stock market's selloff. Generally, if a rally cannot sustain more than 1000 advancers over decliners, it will turn out to be more of a range trade. Observe also how, even after the selloff, we could not sustain a plurality of decliners over advancers, preventing the day from turning into a big downside reversal session.
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