Module 6 - Position, Course & Speed
Measuring Distance on the Chart
Distance is measured using dividers on the latitude scale at the side of the chart. Set the dividers to the distance you want to measure on the chart, then transfer them to the latitude scale. Read the distance in nautical miles and tenths.
Use the latitude scale at roughly the same latitude as the area you're measuring — the scale changes slightly as you move north or south on a Mercator chart.
Divider span
Measure the route first. Do not change the dividers.
Latitude scale
50°24′
23′
22′
21′
20′
For this chartwork measure, read 1′ on the nearby latitude scale as 1 M.
- ALWAYS use the LATITUDE scale (side of chart) for distance
- 1 minute of latitude = 1 nautical mile
- Use the latitude scale at the same latitude as your measurement
- Never use the longitude scale for distance
Practice this in context
Chart distance is only one part of the navigation workflow. The full module connects it to bearings, speed, time, and chartwork practice.