GASCO Calibration Gas 10L-429S 200 PPM Carbon Monoxide, 75 PPM Hydrogen Sulfide, 2.5% Methane (50% LEL), 15% Oxygen, Balance Nitrogen Contained in a 10 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection Built in Aerosal Trigger, Calibration Certificate NIST, Made in the USA