Watlow RELAY MASTER is an enclosed, ON/OFF temperature control that snaps onto a Watlow mercury relay, making it useful for controlling the temperature of various systems and processes. It features a Type "J" thermocouple input, and offers LED indication of energized output (load light) for easy monitoring. The RELAY MASTER provides accurate temperature control with repeatability of +1% of operating span and set point stability, ambient temperature stability, and ambient compensation accuracy not exceeding 5uV/*F or 9uV/*C referred to the input.