GASCO Precision Calibration Gas 58es-428X-20 Mixture 20 PPM Hydrogen Sulfide, 1.45 % Methane,(29 % LEL,(58 % LEL Pentane Equivalent), 15% Oxygen, Balance Nitrogen Contained in a 58L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA