Full sky (120° × 120°) Stokes-I residual images created by using 69 sub-bands and 50–300λ baseline cut, and integrating the full observation after DI calibration, Cas A and Cyg A subtraction, and DD calibration with four different strategies with DDECAL and SAGECAL on the RA 18h flanking field. Shown are the residuals after DI calibration (top left). After DI calibration, all sources are subtracted, including Cas A and Cyg A in one step (i.e. the one-step method, top middle and right), or first Cas A and Cyg A are subtracted (i.e. the two-step method, bottom left) and sources in the centre are subtracted (bottom middle and right). The flux of Cas A and Cyg A is largely reduced after Cas A and Cyg A subtraction (bottom left), while sources in the centre remain. The one-step method with SAGECAL shows comparable performance in Cas A and Cyg A subtraction (top right), while DDECAL still shows a high level of residuals (top middle).