I missed the August 2024 rally by three days. Sitting there watching the S&P 500 rip higher while I was flat — that stung. Then I realized the Zweig Market Breadth Thrust indicator had been screaming BUY for a week. I just wasn't watching it.

The Zweig Market Breadth Thrust indicator is a market-wide oscillator that measures how many NYSE stocks participate in a move. It calculates the ratio of advancing stocks to total moving stocks, then smooths the result with a 10-day exponential moving average. When this ratio crosses above 0.615 or below 0.4, it signals a rare but powerful shift in market internals. Martin Zweig built this to answer whether a market move is broad-based or just a few megacaps fooling everyone.