text: Appendix C
  DIRECTION
  C-30. Direction is the most important element of survey control. The mil relation formula states that one mil
  of error in direction at 1,000 m will result in a one-meter lateral deviation from the target. As the range
  increases, so does the deviation.
  C-31. FA personnel will use the M2A2 aiming circle to perform directional control in a GPS degraded,
  disrupted, or denied environment. Soldiers can perform directional observations using the sun and stars.
  Soldiers can also provide directional control using a declinated lensatic or M2 compass.
  Note. Units equipped with the gun laying and positioning system have an organic capability to
  establish an orienting station and end of the orienting line for the unit.
  ARTILLERY ASTRONOMIC OBSERVATION USING THE SUN
  C-32. Using the aiming circle in the artillery astronomic method of determining azimuth; two sides of the
  Pole-Zenith Star triangle, the polar distance and colatitude, and one angle are used to solve for the azimuth
  angle. This computation is based on the time of the observation. The problem of determining azimuth consists
  of taking a horizontal reading at the observer's station between the mark and sun, the azimuth of which can
  be computed. The simple operation of subtracting this horizontal angle from the computed azimuth of the
  sun gives the desired azimuth to the mark. For more information on this procedure see ATP 3-09.02.
  CAUTION
  The sun must never be viewed through the telescope without a sun filter.
  The filter should be inspected before use to ensure that the coated
  surface is free from scratches or other defects.
  Serious eye damage will result if proper precautions are not taken. If the
  sun filter has been damaged or lost, a solar observation may be
  completed by use of the card method. The image of the sun is projected
  onto a card held 3 to 6 inches behind the eyepiece and the telescope is
  focused so that the cross hairs are clearly defined.
  ARTILLERY ASTRONOMIC OBSERVATION USING A STAR
  C-33. The artillery astronomic method can be used with observations on Polaris or on east-west stars. Used
  with Polaris, this method yields the most accurate azimuths. When the artillery astronomic method is used
  with east-west stars, the requirement for accurate time is a disadvantage, but the method can be used when
  no stars meet the position requirements for the altitude method. Computation of artillery astronomic star is
  the same as the computations for artillery astronomic sun. For more information on artillery astronomic
  observation see ATP 3-09.02.
  MEASURING AN AZIMUTH WITH THE M2 COMPASS
  C-34. To read the azimuth scale by reflection, hold the compass in both hands at eye level with arms braced
  against body and with the rear sight nearest your eyes. Place the cover at an angle of approximately 45° to
  the face of the compass so that the scale reflection can be viewed in the mirror. Level the instrument by
  viewing the circular level in the mirror. Sight on the desired object and read the azimuth indicated on the
  reflected azimuth scale by the south-seeking (black) end of the compass needle. For more information on
  measuring an azimuth with the M2 compass see ATP 3-09.50
  C-35. The M2 compass is an alternate instrument for orienting or laying howitzers. The unmounted magnetic
  compass is a multipurpose instrument used to obtain angle of site and azimuth readings.