USCG Exam PracticePlot true course and distance between two charted points
When measuring distance on a Mercator chart using dividers, against which scale must the measurement be taken?
- A. The longitude scale at the top or bottom of the chart
- B. The compass rose distance scale printed on the chart
- ✓ The latitude scale at the working latitude of the lineCorrect
- D. Any convenient portion of the latitude scale regardless of latitude
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 chart. The longitude scale must never be used for distance measurement.