This part of the standard descrives procedures for testing local thickness by destructive and non-destructive test methods, and for testing average thickness. Thickness determinations depend on the nature of the component or article, the type of coating and service requirements. In some cases, the local thickness of the coating on a specified area may be the basis of acceptance whereas in others the average thickness over the whole significant surface is adequate. Local thickness may be determined by instrumental methods, by localized chemical attack of the coating, or by sectioning and, after suitable preparation, measuring the thickness with a calibrated microscope. Average thickness is the arithmetic mean of a number of local thickness measurements taken over the significant surface of an article or a value calculated from "strip and weighing" methods. The latter may be carried out on a number of small articles or on one large article. Some methods of determining the thickness of a coating are non-destructive, some are destructive to only the coating whereas others are destructive to the article. Where the coating only is damaged the article may frequently be salvaged by re-plating.