Boss OD-3 Owner's Manual page 8

LEVEL Knob
TONE Knob
8
DRIVE Knob
LEVEL Knob
This knob adjusts the level of the effect
sounds.
DRIVE Knob
This adjusts the amount of overdrive.
Rotating it clockwise increases the effect,
whereas counterclockwise rotation reduces
the effect.
TONE Knob
This controls the tone. Rotating the knob
counterclockwise will make the sound
milder, while rotating it clockwise will
make the sound sharper.