Maximum variogram value as a function of the mean G CCD magnitude for known constant and variable sources from the OGLE survey as observed by Gaia. The grey line shows the detection threshold derived from simulated Gaia-like light curves (see Roelens et al. 2017). The brown line corresponds to the same threshold definition scaled by a factor of 10. Panel a: colour-coded by period P_OGLE from the OGLE catalogue, and panel b: colour-coded by IQR from Gaia per-CCD G photometry. It appears that with this detection threshold γ_det = 10γ_det,simu, panel a: majority of constant stars and a significant fraction of longer-period variables are not detected as candidates with short-timescale variability when the variogram is used, and panel b: variable sources that are not detected with the variogram approach are low-amplitude sources.