Marineland's Visi-Therm Deluxe Heater is reliable and accurate. It maintains a temperature within one degree over or under the set temperature. The temperature is easy to set and it lets you know with a "click" sound for every adjustment. The Visi-Therm Deluxe also lets you know when it is working with a clearly visible LED on/off light. Newly designed unit features a double-strength glass casing for extra protection against aggressive aquarium dwellers. Newly designed mounting bracket features three windows for easy visibility of temperature setting.