GFV243 Honeywell Calibration Gas Mixture Equivalent by GASCO Hydrogen Sulfide 25PPM, Carbon Monoxide 50PPM, Methane 2.5% (50% LEL), Oxygen 20.9% contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA