The thermometer is a device that measures temperature or temperature gradient using a variety of different principles. The word thermometer is derived from two smaller word fragments: thermo from the Greek for heat and meter also from Greek, meaning to measure. A thermometer has two important elements: the temperature sensor (e.g. the bulb on a mercury thermometer) in which some physical change occurs with temperature, plus some means of converting this physical change into a value (e.g. the scale on a mercury thermometer). Industrial thermometers commonly use electronic means to provide a digital display or input to a computer.
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Fever (also known as pyrexia, from the Greek pyretos meaning fire, or a febrile response, from the Latin word febris, meaning fever, and archaically known as ague) is a frequent medical symptom that describes an increase in internal body temperature to levels above normal. Fever is most accurately characterized as a temporary elevation in the body's thermoregulatory set-point, usually by about 1–2 °C.