On Wed, 19 Mar 2008 21:28:49 -0500, "Martin H. Eastburn"
wrote:

You are right. The calculation of octane is an average of two calculations.
That is new in the last 15 or so years.

Now the gas has so many odd this and that additives - some up to 50% non-gas.

Once it was 98% or more - mostly lead was added. Or nitro :-)

Martin

Most MN gasoline has a significant percentage of ethanol, and E85 is
widely available.