Difference of LOFAR-HBA 5° × 5° Stokes-I residual images after DD calibration with different calibration scenarios on the RA 18h flanking field at frequency 113.9–127.1 MHz shown in Fig. 3. The images are created with a pixel size of 0.2 arcmin using baselines 50 – 5000λ, combining 69 sub-bands and a single observation night L612832 (~ 11.6-hour). The residual images with different DD calibration scenarios are subtracted by the residual image of the DDECAL and one-step scenario. A reference source is shown (dashed blue circle), which is identical to the one in Fig. 3 to compare different DD calibration residuals.