🔍 Key Concepts

• Relationship between true, magnetic, and compass (T–V–M–D–C) including how variation, gyro error, and deviation fit into that chain • How to use the table of PSC vs PGC to estimate values between listed points (interpolation) • Sign convention: what does W or E mean for variation, deviation, and gyro error when converting between headings

💭 Think About

• First, convert the given gyro heading (058°) into the corresponding true heading, taking the stated gyro error into account. Is the gyro reading too high or too low when the error is west? • Next, from the true heading, work your way down the T–V–M–D–C chain using the known variation 8° W to find the magnetic heading you would expect. • Finally, compare this expected magnetic heading with what the table (using PSC and PGC) implies for a gyro course near 058°. From this comparison, determine the sign (E or W) and approximate size of the deviation.

✅ Before You Answer

• Be very clear whether a west error is added or subtracted when going from gyro to true and from true to gyro. • Check that when you apply 8° W variation, you’re moving in the correct direction between true and magnetic in the T–V–M–D–C chain. • When using the PSC/PGC table, make sure you’re choosing the correct pair of headings to interpolate between and that your final deviation sign (E or W) matches the direction of the difference you observe.