Examples of the three quality classes used for the HI quality assessment. The top row shows an example of a “good” observation (ObsID 190914041, beam 5, cube 2), the middle one an “okay” observation (ObsID 190914041, beam 8, cube 2) and the bottom one a “bad” observation (ObsID 190914041, beam 3, cube 2). The columns show, from left to right, the noise histogram, an extract of the central velocity channel, and a position-velocity diagram through the center of the cube (the horizontal lines in the position-velocity diagrams are the subband edges; see Sect. 7.2). In the left column, the short horizontal line indicates the rms, σ, and the two dotted vertical lines indicate ±6.75σ. The “good” observation in the top row shows hardly any artifacts and a Gaussian noise histogram. The “okay” observation in the middle row shows a minor continuum subtraction artifact, which causes somewhat extended wings to the noise histogram. The “bad” observation in the bottom row shows significant continuum subtraction artifacts, resulting in a very non-Gaussian noise histogram.