Dependence of the scaling function for uncertainty in RV (S_RV) as a function of time between observations. Plot a) shows how scaling parameter A varies with time between repeat observations. Numbers indicate size of the sample used to determine A. Plot b) shows the CDFs of the normalised distribution of RV precision for short-term repeats (black line), long-term repeats (red line) and long term repeats where the observations were taken on the same observing night (blue dashed line). The CDFs for the short-term repeats and the long-term repeats within a night are indistinguishable using a two-tailed Kolmogorov-Smirnov test.