Panels (a) and (b) show the mean meta-correlation result separately with different Δt (Δt = 2, 4, …, 20) for CSI 300 and for S & P 500. The standard deviation is calculated as an error bar. Panels (c) and (d) depict the merge graph of the two sides of the lowest point in corresponding meta-correlation graph. The top red axis and the red data points are shown for the left side, while the bottom axis and green data points are for the right side. The black lines are the best fitting parabolas.