Data with errorbars, phase-folded with our fit including periastron precession, shown in the upper plot. The colours represent different datasets, as in Fig. 1 (see also Sect. 4.2 for more details). Residuals of the periastron precession rate fit are shown in the lower plot. The error-bars include the jitters, as in Table 4. In both plots, the in-transit points are not shown as they were not used in the fit.