Lightcurves at 21 cm of the five brightest field sources in the 21 cm image shown in Fig. 12. The steep spectrum source S1 was used for flux normalization. The modulation indices of the sources are given on the right. The typical uncertainty on the flux densities for the various epochs is dominated by systematic errors, which are estimated to be about 2%. This implies that no believable variations have been detected in sources S4 and S5. All fluxes given are apparent fluxes, uncorrected for the primary beam.