Top: consecutive simulated transits of a planet with an orbital period P_orb = 1.0132P_⋆. Each light curve is affected by spot-crossing events; see text for details. Middle: estimated mid-transit times of the transits in the top panel. The sinusoidal shape of the O−C diagram is the result of spot-crossing anomalies in the transits Ioannidis et al. (2016). Bottom: unsharp masking transit residuals of the planet; note the correlation with the sinusoidal O–C diagram in the middle panel.