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. A separate statute-mile scale printed in the chart title block
- ✓ The latitude scale at the same latitude as the line being measuredCorrect
- D. The latitude scale at the equator, where one degree equals 60 miles
Why C is correct
One minute of latitude equals one nautical mile, but because meridian length varies with latitude on a Mercator chart, distance must be measured on the latitude scale at the working latitude of the line — never on the longitude scale and never at a different latitude.