Charts have been developed that, from the composition of gasoline-engine exhaust, indicate quickly and easily: 1. Fuel-air ratio of the mixture inducted into the engine. 2. Uniformity of mixture distribution and completeness of combustion. 3. Internal consistency of the set of exhaust-composition measurements.Calculation of fuel-air ratio from exhaust composition is common, but the charts have advantages in some applications and less sensitivity to error in CO2 determinations.Determination of mixture uniformity from total exhaust composition appears to be new. The charts provide a worthwhile check on instrument accuracy, which is not an integral part of other F/A techniques.