reference gas #02369OIML 1. Adapted from ISO 7504, 4.1 (calibration gas mixture) and 4.1.1 (reference gas mixture) and “VIM”, 5.13 (reference material) and 5.14 (certified reference material); 2. In the referent ISO Standards, the expression “calibration gas” is generally used; 3. See also Annex B.