A thermometer (frae the Greek θερμός, thermos, meanin "het" an μἐτρον, metron, "measur") is a device that measurs temperatur or temperatur gradient uisin a variety o different principles. A thermometer haes twa important elements: the temperatur sensor (e.g. the bulb on a mercur-in-glass thermometer) in which some pheesical change occurs wi temperatur, plus some means o convertin this pheesical chynge intae a numerical value (e.g. the veesible scale that is marked on a mercur-in-glass thermometer).
Thare are mony types an mony uises for thermometers.