USCG Exam PracticeLatitude, longitude, and geographic coordinates
To plot a true course between two points on a Mercator chart, a mariner walks parallel rulers from the course line to the compass rose. Which ring of the compass rose provides the true course?
- A. The inner ring corrected by the chart's variation note
- B. Either ring, since both are referenced to true north on a Mercator chart
- C. The inner ring, which shows magnetic directions
- ✓ The outer ring, which shows true directionsCorrect
Why D is correct
The outer ring of the compass rose shows true directions referenced to true north. The inner ring shows magnetic directions. True course is read where the parallel ruler crosses the outer ring.
Cited:Bowditch Ch. 4 §406