Left: Width of the distribution of $\Delta \mu_i$ (see text) as a function of the number of \piz\ mesons in sample {\tt S2}, for \glspl{SM} 0-9 (blue, green, cyan) and \glspl{SM} 10-17 (red, orange, yellow), for various $\sigma_{\piz}$ cell selection: $9.6 < \sigma_{\piz} < 11.0$~MeV/$c^2$ (circles), $9.0 < \sigma_{\piz} < 12.0$~MeV/$c^2$ (diamonds) and none (stars). Right:~Statistical uncertainty on the \piz\ meson mass as a function of the number of \piz\ mesons collected in the cell, for \glspl{SM} 0--9 with the tightest (blue) and without (green) selection on $\sigma_{\piz}$ as well as for \glspl{SM} 10--17 with the tightest (red) and without (yellow) selection on $\sigma_{\piz}$.