Class of Survey is a means of categorising the internal quality, or precision of a survey. The number of categories, the notation applied, and the accuracy tolerances defining the transition from one class to another are defined by individual nations. Typically they are based on traditional geodetic surveying categories, supplemented by several extra categories of higher precision applicable to GPS Surveying and GPS Geodesy techniques, and may be different for horizontal surveys and vertical surveys. The attachment of a particular Class "label" (e.g. A, B, etc.) to a survey, comprising a few or many points within a "network", carried out using GPS or any other technique, is performed as part of the process of "network adjustment" in which the relative error ellipses (in the horizontal case) between coordinated stations are computed and compared with the accuracy standards that must be met for various categories of Class. See Minimally Constrained.