text: Appendix A
  of limited visibility. The PLD should be located outside the range where enemy forces can place the attacking
  force under effective direct fire. In figure A-25 on page A-14, PL ROBERT is designated as the PLD.
  Support by Fire Position
  A-58. A support by fire position designates the general position
  from which a unit performs the tactical mission task of support
  by fire (ADP 3-90). Paragraph B-58 defines the tactical mission
  task of support by fire. The purpose of these positions is to
  increase the supported force’s freedom of maneuver by placing
  direct fires on an objective that a friendly force is going to
  assault. Support by fire positions are located within the
  maximum friendly direct fire range of the enemy positions.
  Commanders select them so that a moving assault force does not
  mask its supporting fires. For this reason, support by fire
  positions are normally located on the flank of an assault force, Figure A-29. Support by fire
  elevated above the objective if possible. Support by fire positions position
  are rarely applicable to units larger than company size. When
  used as a planning symbol, the support by fire position depicted in figure A-29 indicates the general location
  and direction from which the unit provides fires. When used as a control measure, the position of the symbol
  dictates the actual location of the position, and the arrows define the left and right limits of the unit’s sector
  of fire.
  Time of Attack
  A-59. The time of attack is the moment the leading elements of the main body cross the line of departure, or
  in a limited-visibility attack, the point of departure (ADP 3-90). Commanders use it when conducting
  simultaneous operations where supporting efforts must accomplish their mission to create conditions for the
  success of the main effort. When determining a time of attack, they consider the time subordinates require
  to—
  * Conduct necessary reconnaissance, prepare plans, and issue orders.
  * Synchronize plans among all subordinate units.
  * Complete attack preparations, such as pre-combat inspections.
  * Move to the LD or PD.
  A-60. Orders normally designate the time of attack as H hour. This occurs when the main body crosses the
  LD. However, H-hour can also designate the time to implement a phase of an operation, such as an airborne
  or air assault phase. The headquarters planning the operation specifies the term’s exact meaning. This is
  usually a part of the unit’s standard operating procedures.
  Zone
  A-61. A zone is an operational area assigned to a unit in the offense that only has rear and lateral boundaries
  (FM 3-0). By not emplacing a boundary to a unit’s front it allows them to move quicker and synchronize
  fires better against the enemy they are facing. A zone is different from an area of operations in that instead
  of a forward boundary to restrict movement and fires a higher headquarters uses maneuver control measures
  and fire support coordination measures. Example control measures to use include things such as a limit of
  advance and a coordinated fire line. Zones are most appropriate for any unit likely to make direct fire contact
  with the enemy during high-tempo offensive operations or when there is a fluid FLOT. Units assigned a zone
  treat areas behind the FLOT as an AO. Zone can be further subdivided as needed into area of operations,
  zones, or sectors as appropriate. Any unit not expecting to be in direct fire contact with the enemy should use
  an area of operations or other means of terrain management. If a unit is attacking in a zone and culminates
  and transitions to a hasty defense, they will continue to use the zone because they eventually expect to go
  back on the offense and the defense is a temporary thing. Figure A-30 depicts a battalion zone for 1-66 Armor.