GASCO Calibration Gas 900es-450BS 60 PPM Carbon Monoxide, 40 PPM Hydrogen Sulfide, 2.5% Methane (50% LEL), 15% Oxygen, Balance Nitrogenn Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA