This International Standard establishes the rating of liquid spark-ignition engine fuel in terms of an arbitrary scale of octane numbers using a standard single-cylinder, four-stroke cycle, variable-compression ratio, carburetted, CFR engine operated at constant speed. Motor octane number (MON) provides a measure of the knock characteristics of motor fuels in automotive engines under severe conditions of operation. The motor octane number provides a measure of the knock characteristics of aviation fuels in aviation piston engines, by using an equation to correlate to aviation-method octane number or performance number (lean-mixture aviation rating). This International Standard is applicable for the entire scale range from 0 MON to 120 MON, but the working range is 40 MON to 120 MON. Typical motor fuel testing is in the range of 80 MON to 90 MON. Typical aviation fuel testing is in the range of 98 MON to 102 MON. This International Standard can be used for oxygenate-containing fuels containing up to 4,0 % (m/m) oxygen. Certain gases and fumes, such as halogenated refrigerants used in air-conditioning equipment that can be present in the area where the CFR engine is located, may have a measurable effect on the MON rating. Electrical power transient voltage or frequency surges or distortion can affect MON ratings. NOTE 1 This International Standard specifies operating conditions I SI units but engine measurements are specified in inch-pound units because these are the units used in the manufacture of the equipment, and thus some references in this International Standard include these units in parenthesis. NOTE 2 For the purposes of this International Standard, the expressions "% (m/m)" and "%(V/V)" are used to represent the mass and volume fractions of a material, respectively.