How r performance octanes(ie, octanes higher than 100%) graded?Extrapolation or some specific test m

Octane number is a reference in respect of detonation in a i.c. engine wen fed with pure octane (a particular hydrocarbon)

If gasoline that is a mixture of hydrocarbon behaves like pure octane in a specially designed i.c. engine, then it is said that has an octane number of 100. If behaves better ther it has an octane number higher than 100...

The worst reference fuel is heptane.

The engine is a Ricardo type engine.