Aerospace Recommended Practice (ARP) 1533 is a procedure for the analysis and evaluation of the measured composition of the exhasut gas from aircraft engines. Measurements of carbon monoxide, carbon dioxide, total hydrocarbon, and the oxides of nitrogen are used to deduce emission indices, fuel-air ratio, combustion efficiency, and exhaust gas thermodynamic properties. The emission indices (EI) are the parameters of critical interest to the engine developers and the atmospheric emissions regulatory agencies because they relate engine performance to environmental impact.