M-508161 Honeywell equivalent Zero Air Calibration Gas GASCO equivalent Zero Air (20.9 % Oxygen balance Nitrogen) 103 Liter C-10 Contains Less than 2 PPM H20, 0.1 PPM THC, 1 PPM CO2, and 1 PPM CO, Cylinder Type: Steel, Connection Type: C-10, Certification NIST, Made in USA