A mercury-in-glass clinical thermometer is a device which is used to measure a patient's temperature. However, there are alternative names for this thermometer such as a mercury thermometer, glass thermometer, or a clinical thermometer. Additionally, this device may be referred to as a medical thermometer or a laboratory thermometer. As technology has advanced, digital thermometers have become more widely used, but the mercury-in-glass clinical thermometer is still commonly used in many medical practices. Whether referred to by one of its numerous names, the function of this thermometer remains vital in monitoring a patient's health and diagnosing illnesses.