A thermometer is a measuring device for determining temperature. Many thermometers work on the basis of the temperature dependency of the expansion of liquids, gases or solid bodies whose expansion coefficient is known. Others make use of the relationship between electrical conductivity and temperature. However, thermometers can also be designed to take advantage of other physical effects that have a temperature dependency. Each thermometer comprises a temperature sensor (for example, a material that exhibits thermal expansion in a particular way) and an indicator device (scale or display). Thermometers are calibrated either on the basis of fixed temperature points or a calibrated reference thermometer.