GASCO Calibration Gas 116L-489-S 40 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 0.5% Methane (10% LEL), 18% Oxygen, Balance Nitrogen Contained in a 116L Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA