This hygrothermograph works without power supply, the value can be read directly, it's widely used for scientific research, workshops etc. Matters need attention: 1. Keep the installation session away from dirt and pollution, the accuracy of the temperature sensor will be effected by dirt, it should be used vertically against the wall. 2. Keep the device away from sources of cold, heat, direct sunlight, place it at a natural ventilation spot. 3. Do not place the device anywhere near steam, the device, otherwise, would not be accurate. 4. Please do not adjust the device randomly since it has been adjusted while manufacturing.