Logarithm of variability amplitude (in mmag) as a function of period. Top panel: the final sample described in Sect. 2. Bottom panel: only stars from luminosity class V. In the colored grids, red represents a greater number of stars, purple indicates a lower number of stars, and black depicts an absence of stars. The distribution of amplitude is shown at the right side of each panel and the period distribution is indicated at the top of each panel.