Part 5/9:
Measuring the angle relative to a horizontal line at the surveyor's location.
Correcting for Earth's curvature using formulas such as ( FG = \frac{D^2}{2R} ), where ( D ) is the distance between points and ( R ) is Earth's radius.
This correction accounts for the fact that on a curved surface, a straight line (the horizontal) appears angled over large distances. Intriguingly, the consistent success of such measurements in real-world applications strongly suggests a spherical Earth, as the calculations rely fundamentally on Earth's curved surface.