Sony PCG-NV200 - Manual (Page 130)

To adjust the volume using the volume dial control
 Rotate the volume dial control clockwise to increase the volume.
 Rotate the volume dial control counterclockwise to decrease the volume.
When you use the Volume icon to increase the volume you also increase the volume dial control volume. Unlike the
Volume icon, the volume dial control adjusts only the sound level from the speakers or headphones.
The volume dial control will work only when the Volume icon is set to an audible level.
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