The word « pattern » has been commonly used to refer to the definitive model of a measuring instrument as well as to the class of instruments that conform to it. The instruments produced by the manufacturer to replicate the pattern constitute a different class. The question of whether an instrument of this class conforms to the pattern is normally the subject of initial verification. Pattern approval not only implies the recognition that the pattern conforms to requirements but, generally, also relates to the instruments of the class produced by the manufacturer; it usually conveys that these may be sold as legal for use and submitted for initial verification.