Preplotting True Azimuth (Zn)

To speed up fix resolution, some navigators preplot the Zn of the bodies. This technique works best when used on a constant scale chart and using a technique of precomputation that gives one assumed position. Before making any observations, plot the assumed position, correct it for Coriolis and precession and/or nutation (if required), and draw the Zn of the bodies through this point. Label each Zn as the 1st, 2d, or 3d as shown in Figure 10-5, or use the name of the bodies. Use arrowheads to identify the direction of the body. Suppose the corrected assumed position is 30°40′ N, 117° 10′ W and the following Zn were computed for the bodies:

1st shot ZN 020°
2d shot ZN 135°
3d shot ZN 270°

Figure 10-5. The fix can be plotted quickly.

Figure 10-5. The fix can be plotted quickly. [click image to enlarge]

The original assumed position of 31° N; 117° 08′ W has been corrected for precession and/or nutation and for Coriolis or rhumb line error to obtain the plotting position. When the first intercept is found to be 10A, second intercept 40A, and the third intercept 50T, the fix may be plotted quickly by constructing perpendicular lines at the correct point on the respective Zn line. This greatly reduces the time necessary to plot the fix.