When you combine the SMS SMART Temperature Probe with the SMS Temperature Sensor it becomes much more versatile. The probe simply plugs into the controller and should hang in the centre of the grow room. When you turn the controller on after installation, it will take 5-10 minutes to scan the room. Using the information it gets, it will evaluate the correct running speed from the fan to maintain the temperature you want. This is where the second dial comes in! The SMS Smart Controller has 60 different fan speeds it can use, so it is a very accurate piece of equipment. They also claim that the new technology inside will lower fan noise, which is also great news! Please be sure to not place the temperature probe in an air flow of a fan. This can cause erratic readings and cause over or under ventilation.