Avgas Octane ratings


#1

Could someone please explain ( slowly :blush: ) Why classic Avgas had two octane ratings and the newer 100LL only one. E.G. 115/145 100/130 and 108/135 ( I think the later was only military?) Was the other one 80/105?
Thanks for your patience.
Be lucky
Stewart


#2

Lean rating followed by the rich rating.

en.wikipedia.org/wiki/Avgas