Reference
Using the Knobs
Basic use of the knobs is to click on them and drag the mouse up and down. However you can obtain different results by holding keys as you drag:
Shift
Values change more slowly as you move the mouse.
Option
The mouse now controls the knob in a rotary style, but only moving to whole number values.
Option+Shift
The mouse controls the knob in a rotary style.
Command
The knob assumes its default position.