A metering body for a chemical injection system comprises a free piston having a pair of mechanically-actuated poppet valves which may individually open to permit fluid to pass from one side of the free piston to the other. By ONOFF control of the switches SW1 to Sw3, the voltage of the first signal line OUTA is changed between a positive voltage level, which is smaller than a voltage V to be applied to a load 20, and the ground level, and the voltage of the second signal line OUTB is changed between the ground level and a negative voltage. A controller conducts an area zoom control such that, when a given area is specified as a sub-area of a predetermined image display region, the acquisition magnification and angle are modified to enlarge the given area. The pipe has no dam or other protuberance to confine the bead of added metal. The multi-purpose missile launcher system is deployed as part of a modular weapon system that mates with a modular bed of the military land vehicle.