GASCO Calibration Gas 74-489S Mixture 40 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 0.5 % Methane (10 % LEL), 18 % Oxygen, Balance Nitrogen Contained in a 74L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA