Properties of α₅₁₀₀. Top panel: Contour (filled by greenish colors) for the correlation between L₅₁₀₀ and α₅₁₀₀ of the selected 3274 SDSS quasars. Circles plus error bars in blue and in red show the results of SDSS J0012-1022 with MJD = 52141 and 56628. Solid and dashed lines in red show the best-fitting results and the corresponding 5σ confidence bands. Contour with reddish levels represents the simulated results. The contour levels in each contour represent 0.1, 0.3, 0.5, 0.7, and 0.9 of the 2D volume contained. Bottom panel: Four examples on periodic variations in α₅₁₀₀ related to sub-pc BBHs, with corresponding six model parameters (log(L₁), log(L₂), α₁, α₂, E₁₀) listed in the same color.