A hygrograph is an instrument used to measure ambient temperature and humidity. Due to the passage of time, the temperature and humidity meter may have inaccurate readings, so it is necessary to perform measurement calibration. Several common methods of hygrometer calibration are described below. Freezing point calibration is a simple and effective method that only requires the use of ice and water to operate. First, pour the pure water into the container, and add enough ice to stir, when the temperature of the water is stable at 0 ° C, the probe of the hygrograph is completely immersed in water, waiting for its stable reading. At this time, the hygrometer should display 0 ° C. If the reading is inaccurate, it can be corrected by adjusting the calibration button on the hygrograph. For details on how to operate the calibration button, please refer to the operating manual of 1 hygrograph. Saturated salt solution method calibration is a relative humidity calibration method, suitable for the relative humidity between 10%- 90% range. First, prepare the saturated salt solution, select the corresponding salt solution according to the required relative humidity, such as sodium sulfate solution can be used for 75% relative humidity calibration. Then, the probe of the hygrograph is completely immersed in the salt solution and wait for it to stabilize the reading. At this time, the hygrograph should display the set relative humidity value. If the reading number 1 is not accurate, it can be corrected by adjusting the calibration button on the hygrograph. The standard temperature and humidity box method calibration is a method with higher accuracy, which is suitable for occasions where the accuracy of the temperature and humidity meter is required. This method requires the use of a standard temperature and humidity box for calibration. First, put the hygrograph into a standard temperature and humidity box, and set the temperature and humidity in the box to known standard values. Wait for the hygrograph to stabilize the reading, compare it with the standard value, and if the reading is inaccurate, it can be corrected by adjusting the calibration button on the hygrograph.