M₀ values obtained from the fit of the 27 realizations (realization number 8 is the one used in Fig. 2). The blue dots are the results of the fits with error bars from iminuit, while the dashed black line shows the M₀ input value of the simulations. The shaded red area is centered on the mean M₀ value ⟨M₀⟩ obtained from the 27 realizations and it shows the uncertainty on ⟨M₀⟩. The shaded yellow area is also centered on ⟨M₀⟩, but shows the average uncertainty along the 27 realization results, ⟨σ_M0²⟩^1/2. Top panel: Fit without velocity error term. Middle panel: Fit with a velocity diagonal error term. Bottom panel: Fit with a full velocity covariance.