Observed minus calculated (O − C) diagram of WASP-12b for all the available transit-timing data. The reference ephemeris here is the linear part of Eq. (4), while the additional quadratic term (based on dP/dE) is plotted as a black solid line. The Asiago data are plotted as black and red points, the remaining points come from the literature: Bai et al. (2022) (red, including TESS), Wong et al. (2022) (light green), Baluev et al. (2019) (light blue), other literature works (pink, available at CDS). Amateur timings from ETD are plotted in gray.