ASTM C1789-14 is a standard test method developed by the American Society for Testing and Materials (ASTM) for calibrating handheld moisture meters for plaster plates, Glass-faced plaster plates, and fiber-reinforced plaster plates. The standard specifies a method for calibrating handheld moisture meters by means of a Conductivity detector and a dielectric meter, using a wet specimen with at least five drying steps, Moisture content is determined based on the ratio of weight loss to dry weight, and a relative humidity (ERH) value is provided for each drying step. The method is designed to improve the accuracy of handheld moisture meters in measuring the moisture content of plaster panels and is suitable for on-site inspections during and after building construction.