MSL101L04 Basic Map Reading SR.pdf lesson 4.pdf

Magnetic azimuth this is determined by using magnetic

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Magnetic azimuth. This is determined by using magnetic instruments such as lensatic and M2 compasses. Field-expedient methods . Several field-expedient methods to determine direction are discussed in Chapter 8. G RID A ZIMUTHS 6-4. When an azimuth is plotted on a map between point A (starting point) and point B (ending point), the points are joined by a straight line. A protractor is used to measure the angle between grid north and the drawn line, and this measured azimuth is the grid azimuth. (See Figure 6-4. The example given represents 99 degrees.) WARNING When measuring azimuths on a map, remember to measure from a starting point to an ending point. If a mistake is made and the reading is taken from the ending point, the grid azimuth is opposite, causing the user to go in the wrong direction.
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Directions 15 November 2013 TC 3-25.26 6-5 Figure 6-4. Measuring an azimuth
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Chapter 6 6-6 TC 3-25.26 15 November 2013 PROTRACTOR 6-5. The various types of protractors include: full circle, half circle, square, and rectangular. (See Figure 6-5.) All of them divide the circle into units of angular measure, and have a scale around the outer edge and an index mark. The index mark is the center of the protractor circle from which all directions are measured. Figure 6-5. Types of protractors
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Directions 15 November 2013 TC 3-25.26 6-7 6-6. The military protractor, GTA 5-2-12, contains two scales: one in degrees (inner scale) and one in mils (outer scale). This protractor represents the azimuth circle. The degree scale is graduated from 0 to 360 degrees, with each tick mark representing one degree. A line from 0 to 180 degrees is called the base line of the protractor. The index (or center) of the protractor is where the base line intersects the horizontal line, between 90 and 270 degrees. (See Figure 6-6.) Figure 6-6. Military protractor 6-7. When using the protractor, the base line is always oriented parallel to a north-south grid line. The 0- or 360-degree mark is always toward the top or north on the map and the 90-degree mark is to the right. To determine the grid azimuth: Draw a line connecting the two points (A and B). Place the index of the protractor at the point where the drawn line crosses a vertical (north-south) grid line. Keeping the index at this point, align the 0- to 180-degree line of the protractor on the vertical grid line. Read the value of the angle from the scale; this is the grid azimuth from point A to point B. (See Figure 6-4.) 6-8. Figure 6-7 shows how to plot an azimuth from a known point on a map: Convert the azimuth from magnetic to grid, if necessary.
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Chapter 6 6-8 TC 3-25.26 15 November 2013 Place the protractor on the map with the index mark at the center of mass of the known point, and the base line parallel to a north-south grid line.
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