MACHINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only ENGINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only PUMPS positive displacement rotary or oscillating piston reciprocating piston or other non-positive displacement This class covers also means for practice or training which may have aspects of simulation, although simulators are generally covered by class . In this class, the following terms or expressions are used with the meanings indicated: "primer" effects the first explosive step in the sequence of explosion; "percussion cap" means a primer which is struck to explode; "igniter" effects the first spark-producing or heat-producing step but may not be explosive; "firing-means" or "initiator" (used respectively in the arts of weaponry and blasting) means a device acting directly on the primer, which device may or may not form part of the fuze; "detonator" or "detonator charge" means a charge used to amplify the explosion of the primer; "fuze" means an assembly or mechanism which incorporates safety and arming means in order that the explosion can only take place under certain conditions; this assembly or mechanism determines also the moment (instantaneous or delayed) or the manner, e.g. impact, proximity, hydrostatic pressure, of the firing; "ammunition" covers propulsive charge and projectile whether or not forming a single body, unless otherwise made clear; "projectile", "missile" or "projectile or missile" means any body which is projected or propelled; "guided missile" means projectile or missile which is guided during at least part of its trajectory; "rocket" means projectile or missile which is self-propelled, during at least part of its trajectory, by a rocket engine, i.e. by a jet-propulsion engine carrying both fuel and oxidant therefor; "fuse" or "fuse cord" means a continuous train of explosive enclosed in a usually flexible cord or cable for setting-off an explosive charge in the art of blasting. FUZE-OPERATING PRINCIPLES Impact Liquid contact Fluid pressure Mechanical force Non-electric time fuzes Electric fuzes Proximity fuzes Combination fuzes FUZES CHARACTERISED BY THE TYPE OF AMMUNITION ARMING OR SAFETY MEANS FUZE-SETTING OTHER DETAILS CHECKING, TESTING SUBJECT MATTER NOT PROVIDED FOR IN OTHER GROUPS OF THIS SUBCLASS