🔍 Key Concepts

• Relationship between gyro heading, true heading, variation, and compass deviation (the classic T–G–M–C relationships) • Meaning of gyro error 2° E and how to correct a gyro reading to obtain true heading • Using nearby entries in a deviation table to estimate deviation at an in-between heading (interpolation)

💭 Think About

• From a given gyro heading and gyro error, what is the true heading? Think about the mnemonic for east/west gyro error (e.g., "gyro least, error east"). • Once you have true heading, how do you use variation 8° W to find the corresponding magnetic heading with no deviation? • Compare the computed magnetic heading with the PSC (standard magnetic compass) value near that gyro heading: does the compass read east or west of magnetic, and by about how much?

✅ Before You Answer

• Be clear on the sign of gyro error 2° E: decide whether you should add or subtract it from the gyro heading to get true. • Apply variation 8° W in the correct direction when converting between true and magnetic (remember how west variation affects magnetic vs true). • Use the PSC/PGC pairs around 166° gyro (on either side of 166°) to judge both the trend and approximate size of deviation; this will help you rule out answers that are too large or with the wrong east/west sign.