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.