🔍 Key Concepts

• Amplitude of a celestial body for finding compass error • Relationship between true bearing, variation, deviation, and compass bearing • Using Moon’s (or Sun’s) computed true bearing at a given time and DR position

💭 Think About

• How do you get from the DR position, date, time, and body (Moon) to a true bearing of that body? What table or sight reduction process would you normally use? • Once you have the true bearing, how do you combine it with variation to get magnetic bearing, and then compare that with the psc (compass) bearing to find deviation? • When you compare magnetic and compass bearings, which direction (E or W) is the deviation if the compass reads higher or lower than the magnetic? Write out a small rule to remember this.

✅ Before You Answer

• Verify you are using upper limb of the Moon correctly when deriving the true bearing (same horizontal bearing, limb only affects altitude). • Be sure that you apply variation with the correct sign (2° W) when converting between true and magnetic. • Carefully check your mnemonic or sign convention for deviation (e.g., "Compass Least, Error East" / "Compass Best, Error West") before choosing between the E and W options.