Single-band residual images produced via per-channel selfcal. The left image is the result of solving for G_p. It is dominated by concentric rings centred on 3C 147 (designated as “A150” here). These are caused by closure errors, and go away once a solution for interferometer-based errors M_pq is done (right image). The remaining artefacts are associated with off-axis sources B, C and D, and are due to DDEs.