The numbers that run along the left side, or vertical axis, of the audiogram represent the loudness level of the tone that was presented.

This loudness is measured in decibels (dB). The smaller the number, the quieter the sound. The larger the number, the louder the sound.

On an audiogram, "0" doesn't mean "off" or "silent". Rather, it is a very quiet volume that was found to be just noticeable to a large number of people with normal hearing.

That's why -10 also appears on an audiogram; some people can hear better than most. In fact, -10 is included in the range of normal hearing for children.

Decibel level on an audiogram typically runs from about -10 dB to 110 or 120 dB.