DM and scintillation drift variations of M53A. From top to bottom: DM measurements from the two observation halves; their absolute differences, with the median and 16th–84th percentile range shown by the red dashed line and shading; intraobservation DM variation rates; and the negative drift rate −μ referenced to 1.5 GHz for the two sub-bands and their weighted averages. Right-hand axes show the corresponding electron-column quantities.