GASCO Precision Calibration Gas 44es-429SP 100 PPM CO, 75 PPM H2S, 15% Oxygen, 25% LEL Methane, 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