Watlow Series 400 is an open board temperature control device with time proportioning or full PID capabilities. It supports inputs from various sensors like Thermocouple, RTD, and thermistor, and has a wide range of output options such as mechanical relay, switched DC voltage, solid-state relay, process output, or Mercury Displacement Relay (MDR) driver. With its adjustable sensitivity, proportional band, cycle time, reset, and rate, this device can be tailored to meet specific temperature control requirements.