GASCO Calibration Gas Equivalent for Portagas 90096140 25PPM H2S, 100 PPM CO, 2.5% CH4, 20.9% O2 in 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