GASCO Calibration Gas 66es-450-B Mixture 100 PPM Carbon Monoxide, 40 PPM Hydrogen Sulfide, 2.2 % Methane, 15 % Oxygen, Balance Nitrogen Contained in a 66L 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