GASCO Calibration Gas 44es-406BS Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.45 % Methane (29 % LEL), 18 % 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