GASCO Calibration Gas 58es-421SO2 100 PPM CARBON MONOXIDE, 25 PPM HYDROGEN SULFIDE, 2.5% METHANE (50% LEL),10 PPM SULFUR DIOXIDE, 18% OXYGEN, BALANCE NITROGEN Balance Nitrogen Contained in a 58L 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