On 20 July your vessel's 1626 zone time DR position is LAT 27°13.0'N, LONG 63°42.0'W, when you take an azimuth of the Sun. Determine the gyro error using the azimuth information. Chronometer time: 08h 24m 18s Chronometer error: slow 02m 12s Gyro bearing: 279.3° Variation: 15°W
• Azimuth of the Sun: converting a gyro bearing to a true bearing to compare with the calculated true azimuth • Chronometer correction: applying chronometer error (slow/fast) to get the correct UTC time for the sight • Difference between gyro error East/West and how it affects the relationship between True and Gyro headings/bearings
• First, work out the correct UTC of the observation using the given chronometer time and error. Then convert from zone time to UTC if needed. • Use the DR position, date, and correct UTC to find the true azimuth of the Sun from tables or calculator. Compare this true azimuth with the observed gyro bearing converted to true. • Think carefully: if Gyro shows more degrees than True, is the gyro error East or West? Use a memory aid like "G-E-T" (Gyro, Error, True) or similar to reason it out.
• Be sure you have the correct sign when applying chronometer error (slow vs fast). • Confirm the zone description/sign (east or west of Greenwich) when converting between zone time and UTC. • Double-check which value is larger, True or Gyro, before deciding if the error is East or West. That sign choice is often where candidates make mistakes.
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