Differential thermometer

Temperature is a physical property of a body that determines the direction of heat flow when the body is brought into contact with another. Heat always flows from a region of higher temperature to one of lower temperature. A standard thermometer measures the temperature of a body with respect to an arbitrary point-usually 0 °C (or, in the USA, 32°F) which is the temperature at which pure water freezes, or 0 K, that is, absolute zero or -273.15 °C. It is, however, not always convenient to measure the temperature with respect to these arbitrary points; many measurements are required to indicate the difference in temperature between two regions or bodies. This may be done with a differential thermometer such as the one described here.