USCG Exam PracticePlotting with variation and deviation (T-V-M-D-C)
When measuring distance on a Mercator chart, the mariner should use which scale?
- A. The longitude scale along the top or bottom of the chart
- B. The compass rose diameter as a reference
- ✓ The latitude scale at the working latitude of the line being measuredCorrect
- D. Any convenient latitude scale regardless of the vessel's position
Why C is correct
One minute of latitude equals one nautical mile, and distance must be measured on the latitude scale at the latitude of the line being measured because meridian length varies with latitude on a Mercator projection. The longitude scale must never be used for distance measurement.