GASCO Calibration Gas 900es-411-SO2 Mixture 100 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 10 PPM Sulfur Dioxide, 0.35 % Pentane (25 % LEL), 19 % 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