O−C diagrams of Kepler Blazhko RR Lyrae stars prepared using the template-fitting method. Red curves represent the main target stars of the Kepler mission, for which the light curves were taken from Benkő et al. (2014). The blue curves represent stars found by Forró et al. (2022) in the background pixels. There can be a difference of four orders of magnitude in the O−C values of individual stars (see vertical scales). The light yellow bars show estimated errors based on a Monte Carlo simulation.