ISO 6141:2015 specifies minimum requirements for the contents of certificates for homogeneous gas mixtures in gas cylinders to be used as calibration gas mixtures. Pure gases, when used as calibration gas mixtures, are also covered by this International Standard. Gases and gas mixtures produced for other purposes are not considered. The requirements in ISO 6141:2015 deal with the metrological aspects of calibration gas mixtures. Other aspects, such as safety and legislative aspects, are not covered. Furthermore, it specifies additional information (optional data) recommended for describing a homogeneous gas mixture, supplied under pressure in a cylinder or other container. It does not cover the field of safety-relevant data and related labelling.