Dependence of the clump mass spectrum on the noise in the datacube of the brightness temperature. The solid line shows the original mass spectrum (with σ_T = 0.19 K), the dashed and dotted lines show spectra obtained from datacubes where the noise was artificially increased by factor 2 and 3, respectively. The dash-dotted line shows the PAGI mass spectrum for the same parameters as in Fig. 5.