This variable speed foot rheostat gives you the flexibility to change speeds while you work. Also gives you greater control over speed rates. To control the entire speed range with your foot, set the PH3 controller speed dial to max and foot rheostat will control from min to max speeds. To limit your speed, set the controller speed dial lower (in the middle or anywhere you like) and the foot rheostat will give you variable speeds up to the level you set on the controller.