USCG Exam PracticePlotting with variation and deviation (T-V-M-D-C)
When measuring distance on a Mercator chart, a 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 portion of the latitude scale regardless of latitude
Why C is correct
One minute of latitude equals one nautical mile, so distance must be measured on the latitude scale at the same latitude as the line being measured. The longitude scale must never be used for distance measurement because meridian spacing varies with latitude on a Mercator chart.