Average sky temperature as a function of the frequency is plotted for the interpolation models as solid lines and for the parameterizations Cane and TKY as dashed lines. The gray band shows the results for the 408 MHz Haslam map when scaled down with a spectral index β between −2.62 and −2.46. The upper plot shows the absolute values, while in the lower plot the results are normalized to those for the scaled Haslam map and a spectral index β = −2.46.