Model RP & Econo-Cal® Calibration Cylinders. Combination gas cylinders contain 60 PPM Carbon Monoxide 1.45% Methane, 15% Oxygen and 20 PPM Hydrogen Sulfide in Nitrogen. For both the Model RP and the Econo-Cal®, contents are at 500psig, and the aluminum cylinders measure 13-3/4" x 3". The Model RP weights 1 lb. 11 oz. and contains approximately 58 liters at atmospheric pressure. The Econo-Cal® weights 1 lb. 1 oz. and contains approximately 34 liters at atmospheric pressure. Reactive gases have an expiration date listed on each cylinder.