Thanks to Rich I now have a drawer in my filing cabinet labeled "Technical Papers"! So I hope I get this correct:
Lang is probably refering to the RON (Research Octane Number). I believe it is commonly used in Europe instead of the MON (Motor Octane Number). The latter being more valid for high-performance applications.
The U.S. octane number is derived from the RON+MON/2 (R+M/2). You will see this formula on gas pumps on the octane label. Our (U.S.) octane number is commonly refered to as the Anti Knock Index, or AKI.
The RON and MON are determined by separate ASTM laboratory tests. Low-speed, low load knock characteristics are determined by the RON test method and high-speed, high heat, high load characteristics are determined by the MON test method. Again, the latter being more pertinent to racing applications.
Rich, feel free to correct away! Sorry for such blatant plagarism!:)