USCG Exam PracticePlotting with variation and deviation (T-V-M-D-C)
After walking parallel rulers from a plotted course line to the compass rose, the mariner reads the true course from which ring of the rose?
- A. The inner ring, which shows magnetic directions corrected for local variation
- ✓ The outer ring, which shows true directions referenced to true northCorrect
- C. Either ring, since both rings are aligned to true north on a corrected chart
- D. The ring whose annual rate of change is printed alongside it
Why B is correct
The outer ring of the compass rose shows true directions referenced to true north. The inner ring shows magnetic directions. When reading a true course after transferring parallel rulers, the mariner reads where the ruler crosses the outer (true) ring.
Cited:Bowditch Ch. 4 §406