Accuracy in flux determination on simulated datasets. Upper panels: full dataset. Lower panels: zoom in the central strips. Left panels: HRI flux determination. Right panels: LRI flux determinations, using different methods. All plots show the quantity (f_meas − f_input)/f_input versus input HRI magnitude: the median offset is consistent with zero in the HRI case, and typically below 5% in the LRI cases. The red dashed line in the bottom left panel refers to a SEXTRACTOR run. See text for details.