GASCO Calibration Gas 44es-498 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 1.62% Methane, (32.4% LEL), (50% LEL Propane Equivalent), Balance Air (20.9% Oxygen balance Nitrogen)n 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