For years, the name "Visi-Therm" has been the industry standard for excellence in aquarium heater performance and reliability. Now there is the Visi-Therm an advanced-design submersible aquarium heater that constitutes the next important step in aquarium heating technology. Water-calibrated to ensure precise temperature selection and superior performance, the Visi-Therm delivers the ultimate in direct-set control, compact double-sealed durability...and certified accuracy to within one degree. With a simple "click" of the dial, you choose the ideal water temperature. Great for turtle tanks.