NavList:

In marine navigation, the Azimuth Angle (Z) is one of the three 'internal' angles in the Navigational Triangle, the other two being the LHA and the Paralactic Angle.

Z is the internal angle at your DR. It is measured from the 'elevated pole' and towards the celestial body (either east and west).

For global navigation, keep in mind that there are four possible orientations of the navigation triangle, so to indicate the correct direction to plot an LOP we add directional labels to Z: A 'prefix' letter (N or S) and a 'suffix' letter (E or W).

The prefix letter has the same name as your 'elevated pole' and indicates the direction 'from' which Z is measured. The suffix letter shows whether the celestial body is east or west of your DR position and indicates the direction 'toward' which Z is measured. Thus,

Z = N ddd.d W (DR Lat N; body W of your DR, LHA <180; measure from N to W)
Z = N ddd.d E (DR Lat N; body E of your DR, LHA >180; measure from N to E)
Z = S ddd.d W (DR Lat S; body W of your DR, LHA <180; measure from S to W)
Z = S ddd.d E (DR Lat S; body E of your DR, LHA >180; measure from S to E)

So, Z = N120.5W tells us the angle is 120.5 degrees, measured 'from' the NP, westward towards the celestial body.

Convention is to convert azimuth angle (Z) to azimuth (Zn) which expresses the angle in the familiar frame of reference that we use to express and plot bearings. Zn is always measured from true north, clockwise through 360 degrees. Thus,

1. DR Lat N, LHA <180: Zn = 360-Z
2. DR Lat N, LHA >180: Zn = Z
3. DR Lat S, LHA <180: Zn = 180+Z
4. DR Lat S, LHA >180: Zn = 180-Z

This is one of those situations where a picture is worth a thousand words. See attached pdf.
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