The most common form of temperature sensor in use is the normal mercury-thermometer. It is mostly used as a doctor’s thermometer for finding out the temperature of a feverish patient. But in some cases i.e. in the high school or college laboratories, they are used for temperature measurement in experiments where the accurate value of temperature is not that important. In this thermometer, the outside temperature expands or contracts the mercury, which by varying its position in the glass tube lets us know the approximate temperature of the surroundings. These are not very accurate but are extremely useful when an approximate value is required.