🔍 Key Concepts

• Mercator sailing relationships between difference of longitude (DLo), meridional parts, and course/distance • How to compute difference of latitude and difference of longitude when one is east and the other is west and in different hemispheres • Using mid-latitude vs. meridional parts to relate departure and DLo to the course

💭 Think About

• First, work out the change in latitude from 11°22'S to 06°52'N and decide if you should add or subtract the degrees and minutes • Then, convert the longitudes 009°18'E and 57°23'W into a total difference of longitude and think about whether you add or subtract when the longitudes are of different names (E/W) • In Mercator sailing, think about how the meridional parts of the two latitudes are used to form the difference in meridional parts, and how that relates to tan(course) and the distance

✅ Before You Answer

• Be sure the difference of longitude is in the correct direction and total degrees/minutes before converting to minutes • Confirm you used difference of latitude (in minutes) and difference of meridional parts in the correct trigonometric function for Mercator sailing (usually involving tan C = Dep / DMP or similar, depending on your method) • After you compute distance, check whether it is reasonable for a trans-Atlantic segment between about 11°S, 9°E and 7°N, 57°W and compare that to the two distance options given