Definition

An exact value (a physical entity or an abstract concept) es­tablished and defined by authori­ty, custom, or common consent, to serve as a refe­rence, model, or rule in measuring quan­tities or quali­ties, es­tablishing practices or procedures, or evalua­ting results. In chart construction, a master copy of a CHART upon which are marked all correc­tions affecting the CHART between printings (U.S. terminol­ogy).