The ISO 13820:2021 standard specifies the basic characteristics and calibrating principles of fixed platen testing equipment for paper, Cardboard and corrugated fiberboard compression testing. The standard describes the structure and working principle of fixed platen compression testing equipment. It requires the equipment to be able to generate compressive force at a constant strain rate, and specifies in detail the upper and lower platen size, parallelism and Smoothness of the equipment. In addition, the standard also clarifies the calibration method and procedure of the equipment to ensure the accuracy and repeatability of the test results. This standard is applicable to a variety of compression tests such as Cardboard Ring Pressure, Corrugated Core Paper Flat Pressure, and Corrugated Fibreboard Edge Pressure. It provides a uniform equipment specification and calibrating basis for the paper and Encasement industries.