What is the purpose of 10 degree drift lines?

The purpose of 10-degree drift lines is to indicate wind drift. These lines are typically used in flight planning and navigation to visually represent how the wind affects an aircraft's flight path. When flying cross-country, pilots must account for wind drift to ensure they stay on course towards their intended destination. The 10-degree increments help pilots to make quick adjustments for heading corrections based on the wind conditions, enhancing their situational awareness and navigational accuracy. This is particularly important during navigation to maintain the correct flight path in relation to ground features or waypoints.

The other options do not accurately reflect the primary function of 10-degree drift lines, as they pertain to different aspects of flight management. For instance, altitude loss would be monitored through different means, ground speed assessed using other flight instruments or calculations, and time enroute determined by considering distance and speed without the direct visual reference that drift lines provide.