This calculator calculates the pump octane, which is the average of the research octane level and the motor octane level or:
(R+M)/2
The pump octane is what is used to label on gas pumps. The research octane is obtained by testing a single cylinder of an engine, which affects low to medium speed knocking and engine run-on. The motor octane is usually the lower number and is found by testing a single cylinder while the engine is under a higher load, such as during when passing. Pump octane can also be referred to as the antiknock Index, or AKI.
Octane is a measure of a gasoline's ability to research engine knock. This is why higher performance engines usually require a higher index value.