Clinical audiograms invert the vertical axis to show hearing loss downward

Evidence

Note that the dBHL scale increases downward to indicate greater hearing loss (a higher amplitude or greater dBHL value needed for the sound to be detected). The 0 dBHL (threshold of hearing) line is thicker than the other lines to give a visual focus on the average threshold of hearing as a reference against which measurements can be compared. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2340

Categorization

• XREF: The downward-increasing dBHL scale inverts conventional plotting; connects to how data visualization conventions encode meaning in medical and engineering contexts.