GASCO 404-17SO2 Calibration Gas, 100 PPM Carbon Monoxide, 50% LEL Methane, 25 PPM Hydrogen Sulfide, 10 PPM SO2, 17% Oxygen, Balance Nitrogen contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA