How to Find True Course, Magnetic Course and Compass Course

Written by brooke ashley
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How to Find True Course, Magnetic Course and Compass Course
Sailors use true, magnetic and compass course to plot their journeys. (sailboat image by brelsbil from

True course, magnetic course and compass course are used for navigating sea vessels and aeroplanes, and are often used in conjunction with each other. Navigators have used these plotting variants for centuries, and today seafarers and pilots use them to correctly pinpoint location, route paths and time necessary to reach a destination. Using True North or Magnetic North as fixed quadrants, you can plot and execute courses based on latitude and longitude.

Skill level:

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Things you need

  • Compass
  • Pencil
  • Geographical charts

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  1. 1

    Set a magnetic compass to True North to achieve the fixed quadrant for a course. Plot this quadrant in a navigation chart and determine the vessel location by taking a compass reading of your current map position. Plot these quadrants on the chart. Then, plot the correct latitude and longitude of the destination on the chart, and take compass readings throughout the journey to reach the destination using an angled line or path. Several factors can influence the performance of a compass, including changes in magnetic fields, and therefore you should plot magnetic course and true course to correct any errors, known as deviations in course plotting.

    How to Find True Course, Magnetic Course and Compass Course
    A compass is used to plot navigational courses, though deviations may need correction. (Compass image by Monika 3 Steps Ahead from
  2. 2

    Determine and plot position based on time and location in relation to fixed, magnetic north quadrants. Use charts plotted from at least two previous years on the exact present time and date as a reference. Adjust any compass readings from compass course that appear to deviate from patterns in prior year charts to determine magnetic course. Magnetic course has been used since the early 19th century, when the electrical currents that originate in the outer core of Earth were first determined to effect navigation. Plot the magnetic course quadrants on the chart to compare with compass course quadrants.

    How to Find True Course, Magnetic Course and Compass Course
    Magnetic north is a fixed set of quadrants from a position in Arctic Canada. (Artic circle image by John Sandoy from
  3. 3

    Plot a Line of Position based upon the compass and magnetic course calculations to achieve true course, which reflects the correct navigational path. You'll plot true course after making corrections to compass course, and taking into account deviations related to magnetic course. To remove any ambiguity and ensure true course, you can create additional lines to correctly plot the fixed position of a destination. These lines, used in mathematical conjunction, form a triangle when plotted correctly.

    How to Find True Course, Magnetic Course and Compass Course
    True course requires correcting any deviants found in compass or magnetic course plotting. (chart plotter image by guiney from

Tips and warnings

  • If plotting becomes tedious, you can use a course conversion calculator to predict correct navigational paths. These calculators are used by the United States Coast Guard.

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