This part of ISO 4628 defines a system for designating the quantity and size of defects and the intensity of changes in appearance of coatings and outlines the general principles of the system used throughout ISO 4628. This system is intended to be used, in particular, for defects caused by ageing and weathering, and for uniform changes such as colour changes, for example yellowing. The other parts of ISO 4628 provide pictorial standards or other means of evaluating particular types of defect. As far as possible, already existing evaluation schemes have been used as the basis. This part of ISO 4628 can also be used for assessing defects not covered by the other parts of ISO 4628.