Best-fit for the radio-X-ray surface brightnesses relation with the lts-linefit method by Cappellari et al. (2013) for the clusters A2744 (left panel) and A523 (right panel). Best-fit parameters and observed intrinsic scatter Δ are indicated in the upper left corner. Red dashed lines indicate 1σ confidence levels, while red dotted lines indicate the 2.6σ confidence levels. Green points indicate the outliers from the best-fit relation (black solid line).