calibration gas mixture

in atmospheric chemistry
https://doi.org/10.1351/goldbook.C00779
A gas mixture of known composition, generally comprising one or more calibration components and a complementary gas.
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2177 (https://doi.org/10.1351/pac199062112167)