That's unnecessary since there's pre-calibrated mixtures referred to, unsurprisingly, as "calibration gas" readily available. Googling for "carbon dioxide cali

That's unnecessary since there's pre-calibrated mixtures referred to, unsurprisingly, as "calibration gas" readily available. Googling for "carbon dioxide calibration gas" will find you what you need as well as the appropriate pressure regulators. Note that even the professional meters require calibration on a regular basis; for example the calibration schedule for the Fluke 975 for CO2 is yearly and for carbon monoxide is monthly.