Fractional difference between the ERCSC flux densities and WMAP flux densities at 30, 44, 70 and 100 GHz. The unit of the abcissa is Jy while the ordinate shows the fractional difference. No correction has been applied to the WMAP flux densities to account for the difference in bandpass compared to Planck. The agreement is good but the significant scatter that can be seen is most likely due to source variability.