Testing on atmospheric parameters using sampling S_const. Top panels: comparison of T_eff, logg and [M/H] estimated from original XP spectra (Y -axis) and APOGEE survey (X-axis). Middle panels: similar to the top panels, but with Y-axis replaced by the results from corrected XP spectra. The color bar in each subfigure displays the number density. Bottom panels: histograms present the differences of T_eff, log ɡ and [M/H] between XP and APOGEE before and after correcting the systematic patterns. The mean values and standard deviations are shown in the labels.