Transit timing variations of KELT-20 b relative to a constant-period ephemeris. The period and midtransit time at the zero epoch are listed in Table 1. Top: data used in the joint fit. Blue points are TESS measurements, and the purple point is the HST/UVIS measurement from Y. Chachan et al. (2025). The solid black curve shows the best-fitting companion model (χ² = 48 for 37 degrees of freedom), and the shaded regions show the 1σ and 2σ predictive intervals. The lower subpanel shows the residuals after subtracting the best-fitting model. Bottom: same model shown over the longer time baseline, including earlier literature midtransit times that were excluded from the fit because of possible lower accuracy. These excluded measurements are shown as black points and listed in Table 2. Most of the earlier measurements are consistent with the model despite not having been included in the fit.