Fitting empirical parameters describing long-term repeats of RV to GES iDR6 data (see Eq. B.2). Plot (a) shows a histogram of E_RV for short- and long-term repeats. Plot (b) shows the variation in the mean value of A as a function of time. Plot (c) shows the variation in A with SNR. Plot (d) compares the cumulative distribution of the normalised measurement uncertainty for long-term repeats E_RV/S_RV (red line) with a unit Gaussian distribution (dashed line) and a ν = 3 Student’s t-distribution (blue circles).