Differences between the Stetson and the Landolt magnitudes for 10 769 stars in common, matching the clean-sample criteria (Sect. 4.1). Each panel reports one of the UBVRI magnitudes as a function of the Landolt B–V, as indicated. The points are colored based on the respective Landolt magnitude, and the median differences with their median absolute deviations are reported in each panel. Horizontal lines and grey-shaded areas mark the zero, ±1, ±3, and ±5% differences. Vertical lines mark the color range covered by the original Landolt (1992) catalogue, which defines the Johnson-Kron-Cousins system. The tail of faint stars extending upwards in the ∆R panel at about B–V =1.5 mag is composed by M dwarfs (although other M dwarfs are well behaved) and could be populated by Hσ emitting stars.