Mercury-in-glass thermometer related to the rapid cooling (and contraction) of the glass. When Celsius decided to use his own temperature scale, he originally defined his scale "upside-down", i.e. he chose to set the boiling point of pure water at 0 °C (212 °F) and the freezing point at -100 °C (-32 °F). One year later, Frenchman Jean-Pierre Christin proposed to invert the scale with the freezing point at and the boiling point at . He named it Centigrade (100 grades). Finally, Celsius proposed a method of calibrating a thermometer: These points are adequate for approximate calibration but both vary with atmospheric pressure.
Medical thermometer There are factors that make readings of this thermometer to some extent unreliable, for example faulty placement in the external ear canal by the operator, and wax blocking the canal. Such error-producing factors usually cause readings to be below the true value, so that a fever can fail to be detected. A temporal artery thermometer, which uses the infrared principle report temperature, were not very accurate and therefore caution should be used. The band thermometer is applied to the patient's brow. It is typically a band coated with different temperature-sensitive markings using plastic strip thermometer or similar technology; at a