Histogram of the distribution of the F₂ statistic of the different fits that are adopted as good ones. The bin width is taken to be 0.25. The cut-off at F₂ =3 corresponds to the adopted threshold. The magenta curve is a Gaussian function corresponding to a zero mean and a dispersion σ= 1. This is the expected behaviour of the F₂ statistic. The blue curve represents a Gaussian with σ = 1.15. This latter function follows rather well the slope of the F₂ histogram on the left side. Broadly speaking, the F₂ function is behaving as expected except for this larger dispersion. Both Gaussian curves were adjusted on the maximum of the histogram and are consequently not normalised on their area. They are drawn to illustrate the explanation in the text.