GASCO Calibration Gas Equivalent for Portagas 10327765 25 PPM H2S, 100 PPM CO, 0.35% C5H12, 19% O2 Balance Nitrogen contained in a 58 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA