GASCO 116ES-413-18 Calibration Gas Mixture, 50 PPM Carbon Monoxide, 50% LEL Methane, 10 PPM Hydrogen Sulfide, 18% Oxygen, in Nitrogen in a 116 Liter ecosmart Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA