🔍 Key Concepts

• Zone descriptions (ZD) and their relationship to time zones (1 hour = 15° of longitude) • How to find the central meridian for a given zone description using ZD × 15° • How to locate the boundary meridians halfway between adjacent central meridians

💭 Think About

• First, calculate the central meridians for ZD -4 and ZD -5, then think about where their midpoint lies in longitude • Decide whether these particular ZD values apply east or west of Greenwich and what sign (E or W) goes with negative zone descriptions in nautical practice • Compare the longitude you find for the dividing meridian with the answer choices and see which one matches in both degrees and E/W

✅ Before You Answer

• Verify that you are using 15° of longitude per hour of zone description • Make sure you are using the correct sign convention: which side of Greenwich corresponds to negative ZD? • Confirm that the boundary between two zones is exactly halfway (7°30') between their central meridians