Way back in the Aviation Myths thread, I posted a graph of German testing of captured allied fuel vs. C3 anb B4 fuels. The rating was based on air fuel mixture, and gave an octane number across the range of mixtures which was expressed as OOZ - Oppau Octane Number.
I was going to do a translation of the German report describing the Oppau Process, turns out some kind soul already did one in 1945: