High-tech electronic aquarium heater you can recalibrate for ultimate temperature control. Jager Thermostat Heater allows easy manual recalibration to ensure precision aquarium temperature regulation. Quality German engineering boosts heater performance for improved efficiency and fully submersible operation in fresh or saltwater aquariums. Shatterproof laboratory glass housing resists cold water shock and thermo-safety control shuts heater off automatically when water level dips too low. ON/OFF indicator light for at-a-glance monitoring of heater operation. Adjustable temperature range from 64°F to 93°F with +/-0.5°F accuracy. Six foot power cord. Maximum outside diameter on all heaters is 1″.