ATP-3-09-30 Observed Fires Download
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Target Location and Identification 28 September 2017 ATP 3-09.30 3-5 Right Add, Left Subtact Rule 3-24. Compute the direction to a target by determining the difference (horizontal angular deviation) in mils between a reference point of known direction and the target, then adding or subtracting the measured difference to the known direction. Direction increases to the right and decreases to the left. Therefore, to determine the direction to the target, apply the number of mils measured right or left of the reference point known direction by use of the right add, left subtract (also called RALS) rule. For example, the azimuth to the reference point is 2,100 mils. The target is 40 mils to the left of the reference point. The direction to the target is 2,060 mils (2,100 - 40). If the target is 60 mils to the right of the reference point, the direction to the target is 2,160 mils (2,100 + 60). Observer-Target Line 3-25. The observer-target line is an imaginary straight line from the observer to the target. It is the most commonly used direction for locating targets and conducting adjustments. Observer-Target Factor 3-26. The observer-target factor is the distance in meters from the observer to the target expressed to the nearest thousand and in thousands. See chapter 5 for a detailed discussion of how to determine the OT factor for distances greater than and less than 1,000 meters. Gun-Target Line 3-27. The gun-target line is an imaginary straight line from gun to target (JP 3-09.3). Angle T 3-28. Angle T is the interior angle formed at the target by the intersection of the observer-target and the gun- target lines with its vertex at the target (TC 3-09.81). If angle T is 500 mils or greater, the FDC should tell the observer. If the observer is told that angle T is 500 mils or greater, at first the observer continues to use the original OT factor to make deviation corrections. If the observer is getting more of a correction than asked for, the observer should consider cutting the corrections to better adjust rounds onto the target. Announced angle T is expressed to the nearest 100 mils. For example, if angle T is 580 mils express and announce angle T as Angle T 600 (see figure 3-3 on page 3-6). METHODS TO DETERMINE DIRECTION 3-29. There are five methods used to determine direction. They are—using automated measuring devices, measuring from a reference point, using a compass, scaling from a map (also use of automated imagery), and estimating. Using Precision Measuring Devices 3-30. When properly calibrated, the laser designator and rangefinder, aiming circle, and other measuring devices can provide direction to the nearest mil. Measuring Form a Reference Point 3-31. Using a reference point with known direction, the observer can measure horizontal angular deviations and apply them to the reference direction. Measure angular deviations with laser range finder, binoculars, or with the hand. If measuring with binoculars, angular deviation is determined to the nearest one mil.