It is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the pyrometric sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model).