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 and training which may have aspects of simulation, e.g. in apparatus for so-called "military games", although simulators are generally covered by class . In this class, the following terms or expressions are used with the meanings indicated: "smallarm" means a firearm which is generally held with one or both hands for firing, but this term also includes a light machine-gun which may be supported on a tripod or the like during firing; "gun" means any weapon having a barrel and a trigger or firing mechanism for projecting a missile; it may be a piece of ordnance or a smallarm. It may use combustible or explosive propellant charges, air pressure, electromagnetism or other propulsive forces; "revolver-type gun" means a gun having a revolving drum magazine, the chambers of which are used successively as firing chamber; "revolver" means a revolver-type pistol; "semi-automatic firearm" means a firearm from which one shot is fired after actuation of the trigger and which then returns to a condition for firing a subsequent shot upon renewed actuation of the trigger; "automatic firearm" means a firearm which will continue firing so long as the initial firing pressure is maintained on the trigger; "sighting" means bringing into visual coincidence a direction defined by a so-called "sighting" device with the direction of a target; "aiming" means bringing a weapon to a direction differing from the sighting direction by corrections in order that the projectile may hit the target; "laying" means setting a weapon in the correct position for hitting a target. Attention is drawn to the definitions of "projectile", "missile" and "rocket" given in Note (2) following the title of class .