The S&P 500 hit the green diagonal lines and a horizontal nodal line of a Gann-inspired diagram for the first time during the decline and is now bouncing higher (see supporting chart in the comment section below).
Additionally 3.8k is the measured move target of the huge rising wedge from last year which broke in September, was retested in Nov then the correction started. So it would make sense for it to be the bottom.
CycleForecast
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Price also hit a lower channel line, a 0.382% Fib retracement level, and the center median line of the blue downward-sloping pitchfork. Loads of confluence at last week's low.
Could have been a simple zigzag pattern with the c-wave ending at those confluence levels but price will have to overcome the red resistance zone to raise the probability.