First panel: optical LCO (g′ and i′) and Al Sadeem (g′, V, and R) light curves of MAXI J1820+070 during its 2018-2019 outburst. Magnitudes are not corrected for reddening. Second panel: Swift/BAT (purple), Swift/XRT (pink), and MAXI/GSC (dark purple) count rates vs MJD. Swift/BAT counts have been divided by 100 for visualisation purposes. Third panel: MJD vs. fractional rms variability amplitude evaluated for the time-resolved optical light curves obtained with the LCO and Al Sadeem observations. Fourth panel: MJD vs. hardness ratio evaluated as BAT/MAXI count rates (HR_BAT/MAXI) and XRT (2–10 keV)/XRT (0.5–2 keV) count rates (HR_XRT). The first panel is available at the CDS.