These knobs generally have a 0 that shuts off the fridge or freezer. They indicate 'cooling strength'. If the device is temperature controlled, you will find an

These knobs generally have a 0 that shuts off the fridge or freezer. They indicate 'cooling strength'. If the device is temperature controlled, you will find an explicit degree F or C symbol. Even without a 0, you can turn the knob in one direction, then the other, and listen when the compressor starts (that's the colder-direction).