SECTOR / DEAD SPACE / ARC / RIGHT / TIME / DISTANCE

"SECTOR"(1) An area designated by boundaries within which a unit
        operates, and for which it is responsible.
        (2) One of the subdivisions of a coastal frontier.  See also "area of
        influence, zone of action."
 

"DEAD SPACE" (1) An area within the maximum range of a weapon, radar, or
        observer, which cannot be covered by fire or observation from a
        particular position because of intervening obstacles, the nature of the
        ground, or the characteristics of the trajectory, or the limitations of
        the pointing capabilities of the weapons.
        (2) An area or zone which is within the range of a radio
        transmitter, but in which a signal is not received.
        (3) The volume of space above and around a gun or guided missile system,
        into which it cannot fire because of mechanical or electronic
        limitations.
 

"ARC"   ok, this one had no concrete definitions, so I did a little
        investigating around the military home pages. They are scary
        places to be.....
 
        Two Possibilities of Abbreviation:
        American (National) Red Cross
        Air Reserve Components
 
        But far more likely was the explanation I found in a Field
        Training Manual Online, describing how a soldier would assess the ground
        situation in combat....

        "Normally, the area nearest the soldier offers the greatest
        potential danger to him. Therefore, the search should begin with the
        terrain nearest the observer's position.  Beginning at either flank, the
        soldier should systematically search the terrain to his front in an
        180-degree arc, 50 meters in depth.  After reaching the opposite flank,
        the soldier should search over a second 50 meter strip, farther out but
        overlapping the first by approximately 10 meters.  The soldier should
        continue surveying in this manner until the entire area has been
        searched."

        So, in this instance, the "left of arc" or "right of arc"
        describes the area immediately before the soldier in ground combat.
        This same section on surveying also gives a lot of information on
        judging distances by size of target, range of weapon fired, etc...
 

"LEFT/RIGHT"    Seemingly obvious, but I thought I'd check
        (1) Terms used to establish the relative position of a body of
        troops. The person using the terms "left" or "right" is assumed to be
        facing in the direction of the enemy, regardless of whether the troops are
        advancing towards or withdrawing from the enemy.
        (2) Correction used in adjusting fire to indicate that a lateral
        shift of the mean point of impact perpendicular to the reference line or
        spotting line is desired.

"TIME"  An epoch, i.e., the designation of an instant on a selected time
        scale, astronomical or atomic.  It is used in the sense of time of day.

"DISTANCE" (1) The space between adjacent individual ships or boats
        measured in any direction between foremasts.
        (2) The space between adjacent men, animals, vehicles, or units in
        a formation measured from front to rear.
        (3) The space between known reference points or a ground observer
        and a target, measured in meters (artillery), in yards (naval gunfire), or
        in units specified by the observer.  See also "interval"