A [[log]] consisting of a [[curve]] which is a continuous record of the temperature [[gradient]] in the borehole. It can be measured by two separate sensors having identical thermal characteristics separated by a fixed vertical distance on a sonde; or, by a technique involving the use of a single temperature sensor and placing the measured [[signal]] into storage so it can be played back after the sensor has moved a distance in the borehole equal to a predetermined vertical distance. The differential temperature [[curve]] enhances small changes in temperature occurring in the borehole. A differential temperature survey should always include a recorded measurement of temperatures in the borehole. See also [[temperature log]].