The relative humidity scale certified with the help of saturated salt solutions is used in hygrometry in the relative humidity (RH) fixed points method. It is a subsidiary scale comprising a number of fixed points reproduced by secondary standards for humidity measurements. The RH fixed points represent some specific RH values that are established at a certain temperature over saturated solutions of salts arising from the hygrostatic properties of such solutions. This standard specifies a set of selected saturated salt solutions whose RH values at a specific temperature correspond to fixed points (or scale marks) of the scale of relative humidity. Moreover, it indicates the conditions under which saturated solutions can be used as hygrostatic solutions. The fixed points method is convenient, inexpensive and reproducible. It is often used for the calibration and checking of instruments that are generally used in industry and research laboratories to measure the relative humidity of air. The use of hygrostatic solutions has also been described in GSO standard to be approved by the organization (1) and GSO standard to be approved by the organization (2) and in national standards [3, 4, 5]. The properties of the solutions and of the water vapor pressure over these solutions have been the subject of numerous studies in a great number of laboratories