Standard deviation (σ) of the logarithmic relative flux density with respect to several parameters. Upper left panel: relation of σ with respect to the signal-to-noise level for sub-samples separated in terciles of distance from the pointing centre and major axis. The different terciles are marked with arrow symbols in the legend: up arrows for the higher tercile, left-right arrows for the middle tercile, and down arrows for the lower one. Upper right panel: relation of σ with respect to the distance to the centre for terciles of major axis and S/N. Lower left panel: relation of σ with respect to the major axis of the sources for terciles of distance to the centre and S/N. Lower right panel: contribution of the calibration effects of the dataset (σ_dataset, as explainedin the text) with respect to the rms noise at 2 square degrees for the individual datasets (coloured circles). The linear fit to the relation is shown as a orange line and its 95 per cent confidence interval as a shaded orange band. The extrapolated location of the final deep image is also marked in the diagram as a green cross.