CG-TR34-1 BW Technologies Calibration Gas Mixture Equivalent by GASCO 100 PPM Carbon Monoxide, 2.5% Methane (50% LEL), 18% O2, Balance Nitrogen contained in a 34 Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA