Observed differential number counts of 500 μm-risers in the HeViCS field (black line) compared to models. Expected values from models are overplotted as coloured lines. Left: comparison of observed and modelled counts. Models are represented by full, coloured lines: cyan for B12 (Béthermin et al. 2012), red for B17 (Béthermin et al. 2017), and green for S16 (Schreiber et al. 2016). The effect of simulated noise is ignored. Right: comparison between observed and modelled counts if the effect of noise is simulated. The effect of confusion and instrumental noise is simulated by adding a random Gaussian noise to the modelled fluxes. Differential counts are then represented by dashed, coloured lines.