GASCO 58L-99-50-100-2.5 Calibration Gas Mixture 50 PPM Hydrogen Sulfide, Carbon Dioxide 100 PPM, Methane 50% LEL (2.5% by Volume) Balance Air in a 58L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA