It is recommended to perform water activity calibration if the measurement result of the saturated salt under the same conditions as sample measurement deviates by more than ±0.02* from the reference value. * Salts are reusable * Do not pierce waterproof breathable film * Recommend to replace after one year To use: Open the lid and set it on the sensor to complete preparation. Please follow the testing standards based upon your sample product. * ISO 18787:2017 - Food Products * ASTM E104 - Pharmaceuticals and Cosmetics SPECIFICATIONS: * Quantity: 1 Each * Type: 0.328 aw, Magnesium Chloride