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ISO Guide 35 explains concepts and provides approaches to the following aspects of the production of reference materials: - the assessment of homogeneity; - the assessment of stability and the management of the risks associated with possible stability issues related to the properties of interest; - the characterization and value assignment of properties of a reference material; - the evaluation of uncertainty for certified values; - the establishment of the metrological traceability of certified property values. The guidance given supports the implementation of ISO 17034. Other approaches may also be used as long as the requirements of ISO 17034 are fulfilled. Brief guidance on the need for commutability assessment (6.11) is given in this document, but no technical details are provided. A brief introduction for the characterization of qualitative properties (9.6 to 9.10) is provided together with brief guidance on sampling such materials for homogeneity tests (Clause 7). However, statistical methods for the assessment of the homogeneity and stability of reference materials for qualitative properties are not covered. This document is also not applicable to multivariate quantities, such as spectral data.