🔍 Key Concepts

• Mid-latitude sailing formulas and when they are used • Relationship between difference of longitude (DLo), difference of latitude (DLat), and course • Use of cosine of mid-latitude when finding departure and distance

💭 Think About

• First, determine the difference in latitude and its sign: are you going north or south? • Then, calculate the difference in longitude and convert it properly to minutes of arc before using it in any formula. • Think about how to use the mid-latitude to adjust the departure: how does the cosine of latitude affect the east–west distance on the earth’s surface?

✅ Before You Answer

• Make sure you correctly compute the mid-latitude (average of the two latitudes) and use its absolute value in trigonometric functions. • Confirm your DLo is expressed in minutes of longitude, not degrees, before applying the mid-latitude sailing formulas. • After computing the distance and course, check if the direction (NW, NE, etc.) you get makes sense based on the change in latitude and longitude.