Human body temperature is well measured by 

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.

Medical thermometers are cleaned before and after each use, with alcohol.

It has a kink which does not allow the mercury level to fall on its own.