Applies to quartz crystal units manufactured as custom-built products or as standard catalogue items and whose quality is assessed on the basis of capability approval. Prescribes the preferred ratings and characteristics, with the appropriate tests and measuring methods contained in the generic specification IEC 1178-1 and gives general performance requirements to be used in detail specifications. Normative annexes A, B, C give example layouts of an abstract of description of capability and of the front page of a CQC specification for process control and of the front page of a CQC specification to demonstrate a boundary or limit.