(1) In this Chapter and in Schedule 2, save where the context otherwise requires -

"additive" means any product (other than hydrocarbon oil, liquefied petroleum gas, substitute fuel or vehicle gas) which may be added to - (a) hydrocarbon oil, (b) liquefied petroleum gas, (c) substitute fuel, or (d) vehicle gas, as an extender or for the purpose of improving performance or for any other purpose, and cognate words shall be construed accordingly;

"agricultural tractor" means a mechanically propelled vehicle which is designed or constructed primarily for use for agricultural purposes;

"ASTM" means ASTM International (formerly known as the American Society for Testing and Materials);