On 9 February your 0739 zone time DR position is LAT 23°31.0'N, LONG 143°41.0'E. At that time, you observe the Sun bearing 104.5°psc. The chronometer reads 09h 37m 12s, and the chronometer error is 01m 52s slow. The variation is 3.5°W. What is the deviation of the standard magnetic compass?
• Converting zone time and chronometer time to the correct GMT of the observation (remember how to apply a slow chronometer error) • Finding the Sun’s true azimuth at the DR position and time, then applying variation to get the magnetic bearing • Using the relationship between compass, magnetic, variation, and deviation (T–V–M–D–C) and keeping the signs (E/W) straight
• How do you combine the chronometer reading, its error (slow), and your zone time to find the exact Greenwich time of the sight needed for the Sun’s GHA and declination? • Once you’ve computed the Sun’s true bearing (true azimuth) at your DR position and time, how do you convert that to a magnetic bearing using the given variation (3.5°W)? • You observed the Sun on 104.5° per standard compass (psc). After you know the Sun’s magnetic bearing, what is the difference between magnetic and compass bearings, and what does the sign of that difference tell you about the deviation (E or W)?
• Confirm you are using 104.5°psc as a compass bearing, not relative or gyro bearing • Be sure you apply westerly variation correctly (remember the T–V–M relationship: how do you go from True to Magnetic when variation is West?) • When you compute deviation, check whether compass is east or west of magnetic and match that to the E or W sign in the answer choices
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