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True, magnetic, and compass headings
23 April 2026 · 15 min · 727 views
What this video covers
A tutorial for PER and Patrón de IATE exam candidates explains the three compass headings used in navigation: true heading (RV), magnetic heading, and compass heading.▶ 0:02 True heading is the angle between the vessel's centerline and the geographic meridian; magnetic heading substitutes the magnetic pole for the geographic pole; compass heading adds the compass's own deviation error on top.▶ 0:57 The formula RV = compass heading + deviation + declination is derived geometrically rather than memorized, using a simple diagram of the true north meridian with magnetic north offset to one side.▶ 5:42 East declination and east deviation carry positive signs; west values carry negative signs.▶ 4:59 Mediterranean charts typically show west declination because magnetic north lies roughly toward northern Canada.▶ 5:46 Compass deviation arises from nearby metal parts or instrument error.▶ 10:00 The tutorial also shows how to reverse the formula — starting from a charted true heading to calculate the compass reading needed to follow that course.▶ 12:23 Working from the true-heading perspective first, then rearranging algebraically, avoids sign errors when converting in either direction.
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