GASCO Calibration Gas 900es-463S-T Mixture 100 PPM Carbon Monoxide, 50 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL), 19 % Oxygen, Balance Nitrogen 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