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2. ISO (2000) Guide 31: Reference materials – contents of certificates and labels. ISO, Geneva, Switzerland
3. ISO (2000) Guide 34: General requirements for the competence of reference material producers. ISO, Geneva, Switzerland
4. ISO (1989) Guide 35: Certification of reference materials – general and statistical principles. ISO, Geneva, Switzerland
5. ISO (1993) Guide to the expression of uncertainty in measurement. ISO, Geneva, Switzerland