Each rifle bullet is programmed, before it is fired, by a second computer in the rifle itself. To determine the distance to the target, the gunman shines a laser rangefinder attached to the rifle at whatever is shielding the enemy. If that enemy is in a ditch, a nearby object—a tree trunk behind or to the side of the ditch, perhaps—will do. Looking through the rifle's telescopic sight, the gunman then estimates the distance from this object to the target. He presses a button near the trigger to add that value to (or subtract it from) the distance determined by the rangefinder.