When should true course measurements on a Sectional Aeronautical Chart be made?

True course measurements on a Sectional Aeronautical Chart should ideally be made at a meridian near the midpoint of the flight route. This practice ensures that the measurement considers the curvature of the Earth and provides a more accurate reading of the true course, especially for longer routes where the Earth's shape can introduce significant deviation.

Measuring at a midpoint allows pilots to assess the true course in relation to the magnetic variation and other navigational influences that may differ between the departure and arrival airports. This is crucial for maintaining accuracy in navigation and ensuring that the flight path is adjusted appropriately as needed.

Choosing other points, such as at the departure or arrival airports, may neglect important factors that affect the course over the entire distance of travel, such as wind effects or changes in magnetic declination. These factors could potentially lead to inaccuracies in the navigation process if only measured at the extremes of the route.