1A310007 CALGAZ Calibration Gas Mixture Equivalent by GASCO 25 PPM Hydrogen Sulfide, 50 PPM Carbon Monoxide, 1.62% Methane, 18% Oxygen Balance Nitrogen contained in a 10 Liter Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder connection Built in Aerosol Trigger, Calibration Certificate NIST, Made in the USA