Results of the wavelet analysis. (a) Optical light curve of BL Lacertae in 2019–2022. The green dashed line represents the flux level corresponding to the median value of the Doppler factor, δ_med = 14.96. (b) Wavelet spectrum for optical light curve. The green dashed line marks a timescale of 2.5 d, which is between those found in high- and low-brightness states with the SF and ACF (see Fig. 11).