Why should true course measurements on a Sectional Aeronautical Chart be made near the midpoint of the course?

True course measurements on a Sectional Aeronautical Chart should ideally be made near the midpoint of the course to account for variations in longitude angles. This approach helps in accurately determining the true course by ensuring that the effects of the Earth's curvature and the changing angles between lines of longitude are minimized. The midpoint serves as a practical reference where the lateral deviations caused by changing latitudes and longitudes are less pronounced, leading to a more consistent and reliable measurement.

By measuring the true course at the midpoint, pilots reduce the risk of significant discrepancies that might arise from making measurements toward the ends of a route, where the angles are more skewed due to the convergence of meridians. Hence, this practice is essential for effective navigation and maintaining accurate flight paths.