GASCO Calibration Gas 650es-410SO2 Mixture 25 PPM Hydrogen Sulfide, 5 PPM Sulfur Dioxide, 0.35 % Pentane (25 % LEL), 19 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection TBD, Calibration Certificate NIST, Made in the USA