GASCO Calibration Gas 900es-406BS Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.45 % Methane (29 % LEL), 18 % Oxygen, Balance Nitrogen Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA