Protractors come in several forms-full circle, half circle, square, and rectangle (fig. 5-33). All of them

Figure 5-34.-Measuring an azimuth on a map.

divide a circle into units of angular measure; and regardless of their shape, they consist of a scale around the outer edge and an index mark The INDEX MARK is the center of the protractor circle from which all the direction lines radiate.

To determine the grid azimuth of a line from one point to another on the map (from A to B or C to D), refer to figure 5-34 as you study the following:

1. Draw a line connecting the two points.

2. Place the index of the protractor at the point where the line crosses a vertical (north-south) grid line.

3. Keeping the index at this point, align the 0-180 line of the protractor on the vertical grid line.

4. Read the value of the angle from the scale; this is the grid azimuth of the point.

To plot a direction line from a known point on a map, refer to figure 5-35 as you study the following:

1. Convert, if necessary, the direction to azimuth.

2. Construct a north-south grid line through the known point. Then proceed in the following steps:

l First, approximately align the 0- 180 line of the protractor in a north-south direction through the known point.

Figure 5-35.-Plotting an azimuth on a map.

l Second, holding the 0 - 180 line of the protractor on the known point, slide the protractor in the north-south direction. Slide it until the horizontal line of the protractor (connecting the protractor index and the 90 tick mark) is aligned on an east-west grid line.

l Draw a line connecting 0, the known point, and 180.

l Holding the 0 - 180 line coincident with this line, slide the protractor index to the known point.

l Make a mark on the map at the required angle.

l Draw a line from the known point through the mark made on the map. This is the GRID DIRECTiON line.