The ISO 11556:2005 standard specifies a method for measuring the curl of paper and Cardboard using a single vertically suspended specimen and defines the relevant terminology. This method is suitable for measuring the curl of paper and Cardboard upon receipt or after exposure to constant climate conditions (e.g. laboratory or printing shop). The curl needs to meet: The curl shape is close to a circular arc, and the curl remains stable during the test. The standard also provides a Measuring method for the curl direction, the angle of the curl shaft, and the size of the curl is calculated. This method helps to evaluate the curl characteristics of paper during processing and use, providing a basis for quality control.