Average fitted background model normalisation as a function of zenith angle ϑ: (a) without zenith-angle interpolation; (b) with zenith-angle interpolation. The normalisation averaged over energy bins is shown for all observations used in the model construction. Boundaries between zenith angle bins as used in the construction of the model are marked by the black dashed lines. The blue markers show the individual observations, whereas the red data points denote the mean and standard deviation in bins of ϑ.