GASCO Calibration Gas 74-470-18 Mixture 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.05 % Propane (50 % 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