GASCO Calibration Gas 650es-450-B Mixture 100 PPM Carbon Monoxide, 40 PPM Hydrogen Sulfide, 2.2 % Methane, 15 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA