Comparison of the simulated and calculated structure function in a similar way as Fig. 8, except the emissivity model is of type beta (spherical β-model gas density). This induces non-stationarity of the projected velocity field, noticeable by the drop at large s. The coloured curves represent the analytical calculation of the mean structure function following Eqs. (12) and (D.3). For simplicity, the variance remains calculated according to Eq. (13), that is assuming Xbeta emissivity with an effective core radius, with θ_eff = 80 kpc.