GASCO Calibration Gas 66es-428-40 60 PPM Carbon Monoxide, 40 PPM Hydrogen Sulfide, 1.45% Methane (29% LEL), 15% Oxygen, Balance Nitrogen n Contained in a 66L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA