The standard "NF EN ISO 1157-1999 Plastics, Cellulose Acetate in Dilute Solutions, Determination of Viscosity Value and Viscosity Rate" specifies a method for evaluating the molecular weight characteristics of cellulose acetate in dilute solutions by measuring its viscosity value and viscosity rate. Viscosity value refers to the flow resistance of a cellulose acetate solution at a specific temperature, in direct proportion to its molecular weight. The standard describes the requirements for test equipment, solution preparation, test conditions and data calculation, ensuring the accuracy and Reliability of test results. The method is widely used in the fields of quality control, production monitoring and research and development of cellulose acetate and its solutions. It helps to characterize the solubility and flow characteristics of materials, thus guiding the processing and application of materials.