GASCO Calibration Gas 650es-417S Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 0.35 % Pentane (25 % LEL), Balance Air Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection TBD, Calibration Certificate NIST, Made in the USA