A thermohydrograph is a scientific instrument that silmultaneously records both temperature and relative humidity in graph form for a preset period of time. These instruments are usually portable and are often used in rooms in art galleries and museums so that the conservators can ensure that the air conditioning is operating correctly [because the preservation of the exhibits is aided by automatically adjusting the air conditioning to maintain close control of temperature and relative humidity and it is necessary to know whether those conditions are being maintained]. These instruments are mechanical with clockwork drives to rotate a drum to which the graph paper is attached. They are relatively delicate and require regular calibration to ensure accuracy.
