The general rule for vertical and lateral corrections is: when the deviation exceeds the amount of mean dispersion, a correction should be made after one round; but if it is equal to or less than this several rounds are fired with the same elevation or deflection, and a correction made according to their mean deviation. The battery commander indicates the length of fuze for time-shrapnel. If firing at artillery and all the guns are equally conspicuous, the fire should be directed upon one of the central guns, otherwise at the most conspicuous gun; if the wind is blowing across the range, the fire should be directed upon the most conspicuous gun on the windward flank. If firing upon masses of troops, the fire should be directed upon the centre of the first line; if firing upon skirmishers, it should be directed first upon one point, then another, close in front of the line. PROJECTILES TO BE USED. =Percussion-shell.=--For ranging, against material, and in default of shrapnel against living targets. Against troops behind loopholed walls,--if it explodes after passing through, use percussion-shrapnel,--stockades, abattis, barricades, entanglements, etc. Direct hits are necessary when it is used against guns, limbers, earthworks, obstacles, etc., and its effects are then due to percussion, penetration, and the explosive force of the bursting-charge. When used against men or horses, it is burst on first graze close in front of the target, and its effects are then produced by its splinters. The smoke made by the large bursting-charge of the percussion-shell aids the observation of fire. The effect of projectiles with percussion-fuzes is dependent on the nature of the ground in front of the target; soft marshy ground, hollows, and cuts diminish its effect, while hard smooth ground increases it. Percussion-shell gives the best results when the fire is concentrated. It can sometimes be advantageously distributed, provided that several guns keep a part of the target under superior fire. =Shrapnel with Time-fuze= is used against all living targets, provided they be not close behind cover, troops behind slight cover, such as shelter-trenches, banks, etc., gun-pits and epaulments, balloons, batteries limbered up or in action, ammunition and other trains, unless firing particularly against the material. With the fuze set at zero it can be used for close defence in default of canister. The effect of shrapnel is due to the penetration of its bullets and splinters; this penetration is small, and it is therefore employed against men and horses only. It has a combination fuze and can be made to burst either in the air or on the first graze, and can therefore be made independent of the nature of the ground in front of the target. Made to burst high by means of its time-fuze, it can be used against living targets behind cover, against which percussion-shell could have but little effect.