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an instrument for the continuous recording of the temperature of air or water.
The sensing element of a thermograph may be a bimetallic strip or a liquid or resistance thermometer. In meteorology, the most common thermograph has a sensor in the form of a bent bimetallic strip, which is deformed upon a change in temperature. The movement of the end of the strip is transmitted to a pointer, which traces a curve on a roll of graph paper. A vertical displacement of 1 mm on the recording corresponds to about 1°C.
A distinction is made between day and week thermographs, depending on the time required for a complete rotation of the recording drum. The operation of a thermograph is monitored by comparison with a mercury thermometer.