This International Standard specifies methods of designating the direction of rotation and the cylinders of reciprocating internal combustion engines and of designating a specific valve in a cylinder head when the cylinder head is mounted on the engine or dismantled. It defines right-hand and left-hand in-line reciprocating internal combustion engines and locations on a reciprocating internal combustion engine so that the position of equipment on the engine can be described. It applies to reciprocating internal combustion engines for land, rail-traction and marine use, excluding engines used to propel agricultural tractors, road vehicles and aircraft. It may by applied to engines used to propel road-construction and earthmoving machines, industrial trucks and for other applications where no suitable International Standard for these engines exists.