The HTP-1500 is the safest and most accurate localized heat therapy system available. Its bright and easy-to-read display provides continuous real-time temperature readings. The digital controller uses proprietary software to manage your prescribed set-point temperature to within one-degree Fahrenheit. Three temperature safety limits guard against the possibility of overheating and the Hi Limit Switches can be tested without taking the unit apart. The HTP-1500 is also Mercury Free. It uses distilled water. HTP-1500 is also directly compatible with Hallowell Heated Hard Pad.