On 11 July your 0240 ZT position is LAT 14°...

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Question 1 of 2066636eea28f7522a1c51aa1b

On 11 July your 0240 ZT position is LAT 14° 52' N, LONG 34° 23' W. You observe Polaris bearing 359.8° pgc. At the time of the observation the helmsman noted that he was heading 279° pgc and 299° psc. The variation is 19° W. What is the deviation for that heading?

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Question 1 of 20

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🔍 Key Concepts

• True–Magnetic–Compass (T–M–C) relationships and the standard diagram: True ↔ Magnetic ↔ Compass • Difference between psc (per standard compass) and pgc (per gyro compass) headings and bearings • Using a known reference (Polaris) to find compass error and then separating it into variation and deviation

💭 Think About

• How does the observed bearing of Polaris (which is very close to true north) help you determine the vessel’s compass error on the standard compass? • You’re given both a gyro heading (pgc) and a standard compass heading (psc) at the same time. Which one is tied directly to deviation, and which one can help you approximate the true heading? • Once you have an approximate true bearing of Polaris and a compass bearing from the standard compass, how do you use the T–M–C chain (including variation) to isolate the deviation term?

✅ Before You Answer

• Be clear which numbers are headings and which are bearings — don’t mix them up. • Remember that variation (19° W) is between True and Magnetic, not between True and Compass. • When you compute compass error, note whether it comes out east or west, then recall the relationship: Compass Error = Variation + Deviation (with proper signs) to solve for deviation.

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