The Geratherm Hypothyroid Basal Thermometer functions in the same way as older mercury thermometers. Contains Galinstan, which is a non-toxic, liquid metal that replaces the toxic mercury. The expanded calibration strip provides an accurate temperature display with a magnifying (optical) case for easy temperature reading. It is suitable for oral or axillary temperature monitoring. Easy to clean or disinfect with alcohol or warm soapy water. Temperature measuring range is 97 degrees F to 101 degrees F. Sold each.