GASCO Calibration Gas 900es-470-18 Mixture 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.05 % Propane (50 % LEL), 18 % Oxygen, Balance Nitrogen Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 660, Calibration Certificate NIST, Made in the USA