The Differential Control feature enables a System 450 control system to monitor and maintain a temperature, pressure, or humidity differential between two sensors of the same type. This feature also enables the control system to control relay outputs, analog outputs, or a combination of relay and analog outputs, based on the sensed differential value relative to user-selected differential values. An example is the water pressure drop across an in-line water filter. See Table 1 for information on the System 450 control modules with this feature.