Kansas Law Dog said:Kathie - It great to have another refiner on the Forum. Two compounds define octane: 1) iso-octane (actually 2,2,4, trimethylpentane, which is 100 octane by definition), and normal heptane (straight chain C7), which is 0 octane by definition. The standards you speak of are mixtures of those two compounds, or another pure compound of known octane value approved by ASTM (American Society of Testing Materials). Just for the record, I wasn't me that said "knocking is caused from watered down gasoline".
KLD- sorry, I know you didn't say it, I was just thanking you for helping explain the hard parts, as I am blonde