On 31 May your vessel's 1420 zone time DR...

Question 1 / 2066636eea28f7522a1c51ae0f

Question 1 of 2066636eea28f7522a1c51ae0f

On 31 May your vessel's 1420 zone time DR position is LAT 29° 06' N, LONG 120° 06' W, when an azimuth of the Sun is observed. The bearing of the Sun per standard magnetic compass was 255.3°. The chronometer time of the observation is 10h 17m 24s. The chronometer error is 02m 32s slow. The variation for this area is 12.9° E. What is the deviation of the standard magnetic compass?

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66636eea28f7522a1c51ae0f

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🔍 Key Concepts

• Chronometer correction and Greenwich Mean Time (GMT) from zone time and chronometer error • Using the DR position, GHA (Greenwich Hour Angle) and declination of the Sun to find its true azimuth/bearing • The relationship between true bearing, variation, magnetic bearing, and compass bearing to solve for deviation

💭 Think About

• First, how do you turn the given zone time, chronometer reading, and chronometer error into the correct GMT for the sight? What sign do you apply to a chronometer that is "slow"? • Once you know the GMT, what tables or data would you use (in real life) to get the Sun’s true azimuth at the given DR position? After you have the true bearing, how do you apply variation to get the magnetic bearing? • After you have the magnetic bearing of the Sun, compare it with the standard compass bearing. Which way (E or W) must the deviation be so that the compass reads what was actually observed?

✅ Before You Answer

• Be sure you have the correct GMT (including the proper sign for chronometer error and the vessel’s time zone) before looking up any Sun data. • Verify that you apply variation with the right sign: remember the common memory aids (e.g., "East is least, West is best") when converting between true and magnetic. • Double‑check whether you are solving for deviation = magnetic – compass or the reverse, and that the E/W sign of the deviation matches the direction of the correction.

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Question 1 of 20

2.5° W

2.9° W

2.9° E

3.2° E

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Question 1 / 2066636eea28f7522a1c51ae0f

Question 1 of 2066636eea28f7522a1c51ae0f

Back

Question 1 of 20

66636eea28f7522a1c51ae0f

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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