the octane rating is the m+s\2 method
it's only menas the fuel's ability to resist detonation
the higher the # the better it is at resisting detonation
don't buy a higher octane gas if your car does not need it
it's useless proly won't do any harm either
i need to use 91 premium because my 5th gen prelude has 10.6:1 compression too high for even 89 octane