GASCO Calibration Gas 34L-406-15 50 PPM Carbon Monoxide, 15 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL), 18 % Oxygen, Balance Nitrogen 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