On 4 July your vessel's 1722 zone time DR...

Question 1 / 2066636eea28f7522a1c51ae1a

Question 1 of 2066636eea28f7522a1c51ae1a

On 4 July your vessel's 1722 zone time DR position is LAT 34°30'S, LONG 174°48'E, when an amplitude of the Sun is observed. The sun's center is on the visible horizon and bears 282° per standard magnetic compass. Variation in the area is 17.2°E. The chronometer reads 05h 21m 48s and is 02m 01s fast. What is the deviation of the compass?

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🔍 Key Concepts

• Amplitude of the Sun and how it is used to find compass error • Correcting the chronometer time (applying the known error) to get correct Greenwich Mean Time (GMT/UT) • Applying variation and deviation: True → Magnetic → Compass (or reverse) and keeping track of East/West signs

💭 Think About

• First, what corrections do you apply to the chronometer reading before using it in any sight reduction or amplitude work? How do you apply a chronometer that is "fast"? • Once you determine the true azimuth (bearing) of the Sun at the time and place of the observation, how do you compare it with the observed compass bearing to obtain the total compass error? • Given the total compass error and the local variation, how do you separate out the deviation? Remember the sign convention for East and West errors.

✅ Before You Answer

• Verify you used the correct date and DR position (latitude and longitude) to obtain the Sun’s declination and local hour angle from the appropriate tables or formulas. • Check that your time conversions are consistent: zone time → GMT/UT → local hour angle, and that the chronometer correction has been applied in the right direction. • Confirm that your final step correctly relates: Compass = Magnetic ± deviation and Magnetic = True ± variation, and that the algebra of signs (E/W) matches your computed total compass error.

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Question 1 of 20

1.5°W

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1.5°E

2.0°E

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Question 1 / 2066636eea28f7522a1c51ae1a

Question 1 of 2066636eea28f7522a1c51ae1a

Back

Question 1 of 20

66636eea28f7522a1c51ae1a

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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