The Penn Plax Therma-Temp Floating Thermometer with Suction Cup is an all glass thermometer with a suction cup mount. The Penn Plax Therma-Temp Floating Thermometer with Suction Cup reads in both Fahrenheit and Celsius. All glass thermometer Suction cup mount Reads in both Fahrenheit and Celsius Temperature range from 20 to 110 F degrees and 10-40 C degrees.