A clinical thermometer is a thermometer used to measure human body temperature. Most old ones use mercury thermometer. It is accurate and sensitive, because it has a narrow place where the mercury level rises very fast.
These thermometers are used in clinics by doctors, so they are also called a doctor's thermometers or medical thermometers. Most of them show both Celsius scale and Fahrenheit temperature scales. The scale runs from 35 degree Celsius to 42 degree Celsius.