GASCO Calibration Gas 44es-414-40 300 PPM Carbon Monoxide, 40 PPM Hydrogen Sulfide, 1.45% Methane, (29% LEL), (58% LEL Pentane Equivalent), 15% Oxygen, Balance Nitrogen Contained in a 44L 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