On 3 October your 0330 zone time (ZD + 5) DR...

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Question 1 of 2066636eea28f7522a1c51adfa

On 3 October your 0330 zone time (ZD + 5) DR position is LAT 47°41'N, LONG 86°49'W. At that time, you observe Polaris bearing 357.5°pgc. The chronometer time of the observation is 08h 32m 04s, and the chronometer is 0m 27s slow. The variation is 5.5°W. What is the gyro error?

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Question 1 of 20

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🔍 Key Concepts

• Polaris as a special star: Its altitude gives you an approximate latitude, and its azimuth is very close to true north. • Converting times: Zone time (ZD +5), GMT/UT, and chronometer corrections all affect GHA (Greenwich Hour Angle) and LHA (Local Hour Angle). • Gyro error concept: Compare the true bearing of the observed object with the bearing read on the gyro compass, then apply the correct sign convention (east or west error).

💭 Think About

• How do you use Polaris to find the true azimuth at your DR position and time, rather than just assuming it is exactly 000°T? • Once you have the true azimuth of Polaris, how do you compare it to the gyro bearing (357.5°pgc) to find the gyro error, and which way (E or W) does the compass ‘point’ compared to true? • How does the variation (5.5°W) help you relate gyro bearings to true directions through the concept of a ‘compass error’ made up of variation and deviation (or gyro error)?

✅ Before You Answer

• Confirm you have correctly applied the chronometer correction (0m 27s slow) to get the correct UTC of the sight. • Verify that you have computed LHA Aries and then the azimuth of Polaris (Zn or Z) using standard sight reduction steps for a meridian‑near star. • Before choosing an answer, check the sign: decide clearly whether the gyro is reading too high or too low compared to true, and translate that into E or W gyro error using the rule “Gyro least, error east; gyro best, error west.”

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