🔍 Key Concepts

• Amplitude of the Moon and how it is used to check compass error • Relationship between true bearing, variation, deviation, and compass bearing (TVMDC) • Effect of east or west variation and deviation on converting between true and compass values

💭 Think About

• From the observed amplitude, what true bearing of the Moon should you expect at that latitude and time of year? Think about whether the Moon should be north or south of the east-west line. • Start with the observed compass bearing and work step-by-step through variation and deviation: in which order do you apply them, and with what signs? • Once you find the total compass error, how do you separate that into known variation and unknown deviation?

✅ Before You Answer

• Be clear about psc (per steering compass) vs. true bearing – do not mix them. • Confirm you are using the correct sign convention: east is usually least, west is best, depending on which way you are converting. • Double-check whether the resulting deviation should be labeled E or W based on whether the compass points too far east or too far west of true.