🔍 Key Concepts

• Relative bearings vs. compass course – how to interpret a light bearing taken on the standard magnetic compass when you already know your steered course on that same compass • Compass error (variation + deviation) – what information you need to actually compute a specific compass error, and what you can or cannot conclude from only one line of position (LOP) and your heading • Local magnetic disturbance vs. bad deviation table – when would an unexpected bearing suggest a temporary local disturbance versus an incorrect permanent deviation card

💭 Think About

• Compare the ship’s compass course (319° C) with the compass bearing (040° C) to the light: what does that tell you about how the compass is behaving, if anything, at that moment? • Ask yourself: with only a course and one bearing on the same standard magnetic compass, can you numerically determine the total compass error (variation + deviation)? What information is still missing? • Think about what would make you suspect a local magnetic disturbance or bad deviation card: what extra evidence would you normally want, beyond a single observed bearing and heading?

✅ Before You Answer

• Verify what data are required to actually calculate compass error (e.g. true bearing from chart, variation, and the observed compass bearing). Do you have all of them here? • Check whether any choice is assuming knowledge of the numerical value or sign of deviation or error that you cannot rigorously compute from the data given. • Confirm which answer choices are definite statements (“you know…”) versus those that only say you should suspect or consider something based on limited information.