🔍 Key Concepts

• Intercept (altitude) sight reduction using a planet (Mars) to find a compass error • Relationship between true bearing, magnetic bearing, compass bearing, variation, and deviation • Correcting a chronometer time that has a known error to get correct Greenwich Hour Angle (GHA) and Local Hour Angle (LHA)

💭 Think About

• How do you convert the observed compass bearing of Mars to a true bearing, step by step, using variation and deviation? Think about the correction order: compass → magnetic → true (or reverse). • Once you have the true bearing from the sight reduction tables (or calculator) and the true bearing from the compass observation, how do you compare them to find the total compass error? • Is the chronometer being fast added to or subtracted from the reading to get the correct UTC, and how does that affect the computed GHA and the resulting true azimuth of Mars?

✅ Before You Answer

• Confirm whether the question is asking specifically for deviation of the standard compass, not total compass error or variation. • Carefully track the signs of variation and deviation (East is least, West is best when going between true and magnetic). • Before choosing an answer, verify you have consistently used the same direction convention (clockwise from north) for all bearings: compass, magnetic, and true.