On 7 April in DR position LAT 27°42.0'N, LONG 114°03.0'W, you observe an amplitude of the Sun. The Sun's center is on the celestial horizon and bears 076°psc. The chronometer reads 02h 10m 17s and is 01m 52s slow. Variation in the area is 8°E. What is the deviation of the standard magnetic compass?
• Amplitude of the Sun and how it is used to find compass error • Sequence of corrections: chronometer correction → GMT → LMT → Sun’s true bearing (azimuth) • Relationship between compass error, variation, and deviation: CE = Var + Dev (with correct east/west signs)
• First, think through how to turn the observed time (chronometer reading and its error) into the correct time to use for the Sun’s calculated true bearing. What key time zone or longitude relationship do you need? • Once you have the Sun’s true bearing at that latitude, date, and longitude, compare it with the compass bearing of the Sun to find the compass error. How do you decide if the error is east or west? • After you know the compass error and you are given the local variation, how do you solve for deviation, again being careful with east/west signs?
• Be sure you are using the correct sign for a slow chronometer and for easterly variation when you apply them. • Confirm you used the DR longitude to find the correct time used in the almanac (zone time vs GMT vs LMT). • Double-check which way to write the relationship: “Compass best, error west; compass least, error east” and how that affects whether you label the final deviation as E or W.
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