Dependence of (d$N_{\rm ch}$/d$\eta)$ / ($\langle N_{\rm part} \rangle$ / 2) on the number of participants for Pb-Pb collisions at $\snn = 2.76$ TeV and Au-Au collisions at $\snn=0.2$ TeV (RHIC average) The scale for the lower-energy data is shown on the right-hand side and differs from the scale for the higher-energy data on the left-hand side by a factor of 2.1 For the Pb-Pb data, uncorrelated uncertainties are indicated by the error bars, while correlated uncertainties are shown as the grey band Statistical errors are negligible The open circles show the values obtained for centrality classes obtained by dividing the 0-10% most central collisions into four, rather than two classes The values for non-single-diffractive and inelastic pp collisions are the results of interpolating between data at 2.36 and 7 TeV.