GASCO 34es-417X-30 Calibration Gas, 25 PPM Hydrogen Sulfide, 0.42 % Pentane (30 % LEL), Balance Air Contained in a 34 Liter Factory Refillable ecosmart Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA