I think most of us know the difference more or less, but I've had some interesting "international" discussions where it broke down because of a lack of understanding about using different scales. People in Europe saying stuff about the "low quality petrol" sold in the US or Canada that was sold with (R+M)/2 (AKI - anti-knock index) as the testing requirement.
I know that they more or less scale a certain way, but it's possible that there are fuels where there's less "spread" between those numbers based on the individual composition. I understand that pure iso-octane fuel has no spread. Or that one fuel with exactly the same (R+M)/2 octane rating might advance timing more compared to another one because the rating is a blunt tool.
I know that they more or less scale a certain way, but it's possible that there are fuels where there's less "spread" between those numbers based on the individual composition. I understand that pure iso-octane fuel has no spread. Or that one fuel with exactly the same (R+M)/2 octane rating might advance timing more compared to another one because the rating is a blunt tool.